[PATCH] RISC-V: For '-march' and '-mabi' options, add 'Negative' property mentions itself.

[Geng Qi <gengqi@linux.alibaba.com>]

When use multi-lib riscv-tool-chain. A bug is triggered when there are two
'-march' at command line.
riscv64-unknown-elf-gcc -march=rv32gcp -mabi=ilp32f -march=rv32gcpzp64 HelloWorld.c
/lhome/gengq/riscv64-linux-ptest/lib/gcc/riscv64-unknown-elf/10.2.0/../../../../riscv64-unknown-elf/bin/ld: /lhome/gengq/riscv64-linux-ptest/lib/gcc/riscv64-unknown-elf/10.2.0/../../../../riscv64-unknown-elf/lib/crt0.o: ABI is incompatible with that of the selected emulation:
  target emulation `elf64-littleriscv' does not match `elf32-littleriscv'
/lhome/gengq/riscv64-linux-ptest/lib/gcc/riscv64-unknown-elf/10.2.0/../../../../riscv64-unknown-elf/bin/ld: failed to merge target specific data of file /lhome/gengq/riscv64-linux-ptest/lib/gcc/riscv64-unknown-elf/10.2.0/../../../../riscv64-unknown-elf/lib/crt0.o
/lhome/gengq/riscv64-linux-ptest/lib/gcc/riscv64-unknown-elf/10.2.0/../../../../riscv64-unknown-elf/bin/ld: /lhome/gengq/riscv64-linux-ptest/lib/gcc/riscv64-unknown-elf/10.2.0/crtbegin.o: ABI is incompatible with that of the selected emulation:
  target emulation `elf64-littleriscv' does not match `elf32-littleriscv'
/lhome/gengq/riscv64-linux-ptest/lib/gcc/riscv64-unknown-elf/10.2.0/../../../../riscv64-unknown-elf/bin/ld: failed to merge target specific data of file /lhome/gengq/riscv64-linux-ptest/lib/gcc/riscv64-unknown-elf/10.2.0/crtbegin.o
......

This patch fix it. And the DIVER would prune the extra '-march' and '-mabi'
options and keep only the last one valid.

gcc/ChangeLog:
	* config/riscv/riscv.opt (march=,mabi=): Negative itself.
---
 gcc/config/riscv/riscv.opt | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/gcc/config/riscv/riscv.opt b/gcc/config/riscv/riscv.opt
index e294e22..5ff85c2 100644
--- a/gcc/config/riscv/riscv.opt
+++ b/gcc/config/riscv/riscv.opt
@@ -38,7 +38,7 @@ Target Var(TARGET_PLT) Init(1)
 When generating -fpic code, allow the use of PLTs. Ignored for fno-pic.
 
 mabi=
-Target RejectNegative Joined Enum(abi_type) Var(riscv_abi) Init(ABI_ILP32)
+Target RejectNegative Joined Enum(abi_type) Var(riscv_abi) Init(ABI_ILP32) Negative(mabi=)
 Specify integer and floating-point calling convention.
 
 mpreferred-stack-boundary=
@@ -79,7 +79,7 @@ Target Mask(DIV)
 Use hardware instructions for integer division.
 
 march=
-Target RejectNegative Joined
+Target RejectNegative Joined Negative(march=)
 -march=	Generate code for given RISC-V ISA (e.g. RV64IM).  ISA strings must be
 lower-case.
 
-- 
2.7.4