Silence nds32 pic warnings

Silence nds32 pic warnings

Fixes:
FAIL: Build pr22471a.so
FAIL: Build pr22471b.so
FAIL: Build pr22649-1.so
FAIL: Build pr22649-2c.so
FAIL: Build pr22649-2d.so
FAIL: PR ld/20828 dynamic symbols with section GC (auxiliary shared library)
FAIL: PR ld/20828 dynamic symbols with section GC (plain)
FAIL: PR ld/20828 dynamic symbols with section GC (version script)
FAIL: PR ld/20828 dynamic symbols with section GC (versioned shared library)
FAIL: PR ld/20828 dynamic symbols with section GC (versioned)
FAIL: PR ld/21233 dynamic symbols with section GC (auxiliary shared library)
FAIL: Build pr22150.so
FAIL: Build shared library for pr14170
FAIL: PR ld/21703 shared
FAIL: Build shared library for broken linker script test
FAIL: Build pr17068.so
FAIL: -Bsymbolic-functions
FAIL: Build pr20995.so
FAIL: Build pr20995-2.so
FAIL: Build pr22374 shared library

	* testsuite/ld-elf/shared.exp (AFLAGS_PIC): Add -mpic for nds32.