RISC-V: Add configure option: --with-multilib-generator to flexible config multi-lib settings.

 - Able to configure complex multi-lib rule in configure time, without modify
   any in-tree source.

 - I was consider to implmenet this into `--with-multilib-list` option,
   but I am not sure who will using that with riscv*-*-elf*, so I decide to
   using another option name for that.

 - --with-multilib-generator will pass arguments to multilib-generator, and
   then using the generated multi-lib config file to build the toolchain.

   e.g. Build riscv gcc, default arch/abi is rv64gc/lp64, and build multilib
       for rv32imafd/ilp32 and rv32i/ilp32; rv32ic/ilp32 will reuse
       rv32i/ilp32.
    $ <GCC-SRC>/configure \
       --target=riscv64-elf \
       --with-arch=rv64gc --with-abi=lp64 \
       --with-multilib-generator=rv32i-ilp32--c;rv32imafd-ilp32--

V3 Changes:

 - Rename --with-multilib-config to --with-multilib-generator
 - Check --with-multilib-generator and --with-multilib-list can't be used at
   same time.

V2 Changes:

 - Fix --with-multilib-config hanling on non riscv*-*-elf* triple.

gcc/ChangeLog:

	* config.gcc (riscv*-*-*): Handle --with-multilib-generator.
	* configure: Regen.
	* configure.ac: Add --with-multilib-generator.
	* config/riscv/multilib-generator: Exit when parsing arch string error.
	* config/riscv/t-withmultilib-generator: New.
	* doc/install.texi: Document --with-multilib-generator.

1 files changed, 31 insertions, 0 deletions

diff --git a/gcc/doc/install.texi b/gcc/doc/install.texi
index 5330bf3..ed737d1 100644
--- a/gcc/doc/install.texi
+++ b/gcc/doc/install.texi
@@ -1252,6 +1252,37 @@ If @option{--with-multilib-list} is not given, then only 32-bit and
 64-bit run-time libraries will be enabled.
 @end table
 
+@item --with-multilib-generator=@var{config}
+Specify what multilibs to build.  @var{config} is a semicolon separated list of
+values, possibly consisting of a single value.  Currently only implemented
+for riscv*-*-elf*.  The accepted values and meanings are given below.
+
+
+Every config is constructed with four components: architecture string, ABI,
+reuse rule with architecture string and reuse rule with sub-extension.
+
+Example 1: Add multi-lib suppport for rv32i with ilp32.
+@smallexample
+rv32i-ilp32--
+@end smallexample
+
+Example 2: Add multi-lib suppport for rv32i with ilp32 and rv32imafd with ilp32.
+@smallexample
+rv32i-ilp32--;rv32imafd-ilp32--
+@end smallexample
+
+Example 3: Add multi-lib suppport for rv32i with ilp32; rv32im with ilp32 and
+rv32ic with ilp32 will reuse this multi-lib set.
+@smallexample
+rv32i-ilp32-rv32im-c
+@end smallexample
+
+Example 4: Add multi-lib suppport for rv64ima with lp64; rv64imaf with lp64,
+rv64imac with lp64 and rv64imafc with lp64 will reuse this multi-lib set.
+@smallexample
+rv64ima-lp64--f,c,fc
+@end smallexample
+
 @item --with-endian=@var{endians}
 Specify what endians to use.
 Currently only implemented for sh*-*-*.