sparc/sparc64: use crtendS.o for default-pie executables [PR96190]

sparc/sparc64: use crtendS.o for default-pie executables [PR96190]

In --enable-default-pie mode compiler should switch from
using crtend.o to crtendS.o. On sparc it is especially important
because crtend.o contains PIC-unfriendly code.

We use GNU_USER_TARGET_ENDFILE_SPEC as a baseline spec to get
crtendS.o instead of crtend.o in !no-pie mode.

gcc:

2020-07-14  Sergei Trofimovich  <siarheit@google.com>

	PR target/96190
	* config/sparc/linux.h (ENDFILE_SPEC): Use GNU_USER_TARGET_ENDFILE_SPEC
	to get crtendS.o for !no-pie mode.
	* config/sparc/linux64.h (ENDFILE_SPEC): Ditto.