[testsuite] [arm] add effective target and options for pacbti tests

[testsuite] [arm] add effective target and options for pacbti tests

arm pac and bti tests that use -march=armv8.1-m.main get an implicit
-mthumb, that is incompatible with vxworks kernel mode.  Declaring the
requirement for a 8.1-m.main-compatible toolchain is enough to avoid
those fails, because the toolchain feature test fails in kernel mode,
but taking the -march options from the standardized arch tests, after
testing for support for the corresponding effective target, makes it
generally safer, and enables us to drop skip directives and extraneous
option variants.

for  gcc/testsuite/ChangeLog

	* gcc.target/arm/bti-1.c: Require arch, use its opts, drop skip.
	* gcc.target/arm/bti-2.c: Likewise.
	* gcc.target/arm/acle/pacbti-m-predef-11.c: Likewise.
	* gcc.target/arm/acle/pacbti-m-predef-12.c: Likewise.
	* gcc.target/arm/acle/pacbti-m-predef-7.c: Likewise.
	* g++.target/arm/pac-1.C: Likewise.  Drop +mve.