RISC-V: Work around bare apostrophe in error string.

RISC-V: Work around bare apostrophe in error string.

An unquoted apostrophe slipped through when testing the recent
V/M extension patch.  This, again, re-words the message to
"Currently the 'V' implementation requires the 'M' extension".

Going to commit as obvious after testing.

gcc/ChangeLog:

	* config/riscv/riscv.cc (riscv_override_options_internal):
	Reword error string without apostrophe.

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/rvv/base/pr116036.c: Adjust expected error
	string.