libcpp: dependency emission tidying

This patch cleans up the interface to the dependency generation a
little.  We now only check the option in one place, and the
cpp_get_deps function returns nullptr if there are no dependencies.  I
also reworded the -MT and -MQ help text to be make agnostic -- as
there are ideas about emitting, say, JSON.

	libcpp/
	* include/mkdeps.h: Include cpplib.h
	(deps_write): Adjust first parm type.
	* mkdeps.c: Include internal.h
	(make_write): Adjust first parm type.  Check phony option
	directly.
	(deps_write): Adjust first parm type.
	* init.c (cpp_read_main_file): Use get_deps.
	* directives.c (cpp_get_deps): Check option before initializing.
	gcc/c-family/
	* c.opt (MQ,MT): Reword description to be make-agnostic.
	gcc/fortran/
	* cpp.c (gfc_cpp_add_dep): Only add dependency if we're recording
	them.
	(gfc_cpp_init): Likewise for target.

1 files changed, 6 insertions, 4 deletions

diff --git a/gcc/fortran/cpp.c b/gcc/fortran/cpp.c
index dcde557..51baf141 100644
--- a/gcc/fortran/cpp.c
+++ b/gcc/fortran/cpp.c
@@ -222,13 +222,15 @@ void
 gfc_cpp_add_dep (const char *name, bool system)
 {
   if (!gfc_cpp_option.deps_skip_system || !system)
-    deps_add_dep (cpp_get_deps (cpp_in), name);
+    if (mkdeps *deps = cpp_get_deps (cpp_in))
+      deps_add_dep (deps, name);
 }
 
 void
 gfc_cpp_add_target (const char *name)
 {
-  deps_add_target (cpp_get_deps (cpp_in), name, 0);
+  if (mkdeps *deps = cpp_get_deps (cpp_in))
+    deps_add_target (deps, name, 0);
 }
 
 
@@ -605,8 +607,8 @@ gfc_cpp_init (void)
 	    cpp_assert (cpp_in, opt->arg);
 	}
       else if (opt->code == OPT_MT || opt->code == OPT_MQ)
-	deps_add_target (cpp_get_deps (cpp_in),
-			 opt->arg, opt->code == OPT_MQ);
+	if (mkdeps *deps = cpp_get_deps (cpp_in))
+	  deps_add_target (deps, opt->arg, opt->code == OPT_MQ);
     }
 
   /* Pre-defined macros for non-required INTEGER kind types.  */