Add '-Wno-complain-wrong-lang', and use it in 'gcc/testsuite/lib/target-supports.exp:check_compile' and elsewhere

I noticed that GCC/Rust recently lost all LTO variants in torture testing:

     PASS: rust/compile/torture/all_doc_comment_line_blocks.rs   -O0  (test for excess errors)
     PASS: rust/compile/torture/all_doc_comment_line_blocks.rs   -O1  (test for excess errors)
     PASS: rust/compile/torture/all_doc_comment_line_blocks.rs   -O2  (test for excess errors)
    -PASS: rust/compile/torture/all_doc_comment_line_blocks.rs   -O2 -flto -fno-use-linker-plugin -flto-partition=none  (test for excess errors)
    -PASS: rust/compile/torture/all_doc_comment_line_blocks.rs   -O2 -flto -fuse-linker-plugin -fno-fat-lto-objects  (test for excess errors)
     PASS: rust/compile/torture/all_doc_comment_line_blocks.rs   -O3 -g  (test for excess errors)
     PASS: rust/compile/torture/all_doc_comment_line_blocks.rs   -Os  (test for excess errors)

Etc.

The reason is that when probing for availability of LTO, we run into:

    spawn [...]/build-gcc/gcc/testsuite/rust/../../gccrs -B[...]/build-gcc/gcc/testsuite/rust/../../ -fdiagnostics-plain-output -frust-incomplete-and-experimental-compiler-do-not-use -flto -c -o lto8274.o lto8274.c
    cc1: warning: command-line option '-frust-incomplete-and-experimental-compiler-do-not-use' is valid for Rust but not for C

For GCC/Rust testing, this flag is (as of recently) defaulted in
'gcc/testsuite/lib/rust.exp:rust_init':

    lappend ALWAYS_RUSTFLAGS "additional_flags=-frust-incomplete-and-experimental-compiler-do-not-use"

A few more "command-line option [...] is valid for [...] but not for [...]"
instances were found in the test suite logs, when more than one language is
involved.

With '-Wno-complain-wrong-lang' used in
'gcc/testsuite/lib/target-supports.exp:check_compile', we get back:

     PASS: rust/compile/torture/all_doc_comment_line_blocks.rs   -O0  (test for excess errors)
     PASS: rust/compile/torture/all_doc_comment_line_blocks.rs   -O1  (test for excess errors)
     PASS: rust/compile/torture/all_doc_comment_line_blocks.rs   -O2  (test for excess errors)
    +PASS: rust/compile/torture/all_doc_comment_line_blocks.rs   -O2 -flto -fno-use-linker-plugin -flto-partition=none  (test for excess errors)
    +PASS: rust/compile/torture/all_doc_comment_line_blocks.rs   -O2 -flto -fuse-linker-plugin -fno-fat-lto-objects  (test for excess errors)
     PASS: rust/compile/torture/all_doc_comment_line_blocks.rs   -O3 -g  (test for excess errors)
     PASS: rust/compile/torture/all_doc_comment_line_blocks.rs   -Os  (test for excess errors)

Etc., and in total:

                    === rust Summary for unix ===

    # of expected passes            [-4990-]{+6718+}
    # of expected failures          [-39-]{+51+}

Anything that 'gcc/opts-global.cc:complain_wrong_lang' might do is cut
short by '-Wno-complain-wrong-lang', not just the one 'warning'
diagnostic.  This corresponds to what already exists via
'lang_hooks.complain_wrong_lang_p'.

The 'gcc/opts-common.cc:prune_options' changes follow the same rationale
as PR67640 "driver passes -fdiagnostics-color= always last": we need to
process '-Wno-complain-wrong-lang' early, so that it properly affects
other options appearing before it on the command line.

	gcc/
	* common.opt (-Wcomplain-wrong-lang): New.
	* doc/invoke.texi (-Wno-complain-wrong-lang): Document it.
	* opts-common.cc (prune_options): Handle it.
	* opts-global.cc (complain_wrong_lang): Use it.
	gcc/testsuite/
	* gcc.dg/Wcomplain-wrong-lang-1.c: New.
	* gcc.dg/Wcomplain-wrong-lang-2.c: Likewise.
	* gcc.dg/Wcomplain-wrong-lang-3.c: Likewise.
	* gcc.dg/Wcomplain-wrong-lang-4.c: Likewise.
	* gcc.dg/Wcomplain-wrong-lang-5.c: Likewise.
	* lib/target-supports.exp (check_compile): Use
	'-Wno-complain-wrong-lang'.
	* g++.dg/abi/empty12.C: Likewise.
	* g++.dg/abi/empty13.C: Likewise.
	* g++.dg/abi/empty14.C: Likewise.
	* g++.dg/abi/empty15.C: Likewise.
	* g++.dg/abi/empty16.C: Likewise.
	* g++.dg/abi/empty17.C: Likewise.
	* g++.dg/abi/empty18.C: Likewise.
	* g++.dg/abi/empty19.C: Likewise.
	* g++.dg/abi/empty22.C: Likewise.
	* g++.dg/abi/empty25.C: Likewise.
	* g++.dg/abi/empty26.C: Likewise.
	* gfortran.dg/bind-c-contiguous-1.f90: Likewise.
	* gfortran.dg/bind-c-contiguous-4.f90: Likewise.
	* gfortran.dg/bind-c-contiguous-5.f90: Likewise.
	libgomp/
	* testsuite/libgomp.fortran/alloc-10.f90: Use
	'-Wno-complain-wrong-lang'.
	* testsuite/libgomp.fortran/alloc-11.f90: Likewise.
	* testsuite/libgomp.fortran/alloc-7.f90: Likewise.
	* testsuite/libgomp.fortran/alloc-9.f90: Likewise.
	* testsuite/libgomp.fortran/allocate-1.f90: Likewise.
	* testsuite/libgomp.fortran/depend-4.f90: Likewise.
	* testsuite/libgomp.fortran/depend-5.f90: Likewise.
	* testsuite/libgomp.fortran/depend-6.f90: Likewise.
	* testsuite/libgomp.fortran/depend-7.f90: Likewise.
	* testsuite/libgomp.fortran/depend-inoutset-1.f90: Likewise.
	* testsuite/libgomp.fortran/examples-4/declare_target-1.f90:
	Likewise.
	* testsuite/libgomp.fortran/examples-4/declare_target-2.f90:
	Likewise.
	* testsuite/libgomp.fortran/order-reproducible-1.f90: Likewise.
	* testsuite/libgomp.fortran/order-reproducible-2.f90: Likewise.
	* testsuite/libgomp.oacc-fortran/parallel-dims.f90: Likewise.
	* testsuite/libgomp.fortran/task-detach-6.f90: Remove left-over
	'dg-prune-output'.

1 files changed, 20 insertions, 0 deletions

diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index bcf8510..a7ec1a9 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -343,6 +343,7 @@ Objective-C and Objective-C++ Dialects}.
 -Wcast-align  -Wcast-align=strict  -Wcast-function-type  -Wcast-qual  @gol
 -Wchar-subscripts @gol
 -Wclobbered  -Wcomment @gol
+-Wno-complain-wrong-lang @gol
 -Wconversion  -Wno-coverage-mismatch  -Wno-cpp @gol
 -Wdangling-else  -Wdangling-pointer  -Wdangling-pointer=@var{n}  @gol
 -Wdate-time @gol
@@ -8944,6 +8945,25 @@ programs.
 Warn for variables that might be changed by @code{longjmp} or
 @code{vfork}.  This warning is also enabled by @option{-Wextra}.
 
+@item -Wno-complain-wrong-lang
+@opindex Wcomplain-wrong-lang
+@opindex Wno-complain-wrong-lang
+By default, language front ends complain when a command-line option is
+valid, but not applicable to that front end.
+This may be disabled with @option{-Wno-complain-wrong-lang},
+which is mostly useful when invoking a single compiler driver for
+multiple source files written in different languages, for example:
+
+@smallexample
+$ g++ -fno-rtti a.cc b.f90
+@end smallexample
+
+The driver @file{g++} invokes the C++ front end to compile @file{a.cc}
+and the Fortran front end to compile @file{b.f90}.
+The latter front end diagnoses
+@samp{f951: Warning: command-line option '-fno-rtti' is valid for C++/D/ObjC++ but not for Fortran},
+which may be disabled with @option{-Wno-complain-wrong-lang}.
+
 @item -Wconversion
 @opindex Wconversion
 @opindex Wno-conversion