RISC-V: Fix accidental embedded -shared regressions.

RISC-V: Fix accidental embedded -shared regressions.

	ld/
	* testsuite/ld-riscv-elf/c-lui.d: Don't use -shared.  Check for _start
	instead of .text.
	* testsuite/ld-riscv-elf/c-lui.s: Add _start label.
	* testsuite/ld-riscv-elf/ld-riscv-elf.exp: Before __global_pointer$
	tests, add call to check_shared_lib_support.