Test: Move target independent test cases to gcc.dg/torture

Test: Move target independent test cases to gcc.dg/torture

The test cases of pr115387 are target independent,  at least x86
and riscv are able to reproduce.  Thus,  move these cases to
the gcc.dg/torture.

The below test suites are passed.
1. The rv64gcv fully regression test.
2. The x86 fully regression test.

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/pr115387-1.c: Move to...
	* gcc.dg/torture/pr115387-1.c: ...here.
	* gcc.target/riscv/pr115387-2.c: Move to...
	* gcc.dg/torture/pr115387-2.c: ...here.

Signed-off-by: Pan Li <pan2.li@intel.com>