ld: Skip unsupported static executable tests

ld: Skip unsupported static executable tests

Skip static executable tests if static executable is unsupported.
Tested on Linux/x86 without libc.a.

	PR ld/22732
	* testsuite/config/default.exp (STATIC_LDFLAGS): New.  Set to
	"-static" if target compiler supports it.
	* testsuite/ld-bootstrap/bootstrap.exp: Skip static executable
	tests if target compiler doesn't support it.
	* testsuite/ld-ifunc/ifunc.exp: Likewise.
	* testsuite/lib/ld-lib.exp (run_ld_link_exec_tests): Likewise.
	(run_cc_link_tests): Likewise.