Compile gcrt1.o with -fPIC

We compile gcrt1.o with -fPIC to support both "gcc -pg" and "gcc -pie -pg".

	[BZ #17836]
	* csu/Makefile (extra-objs): Add gmon-start.o if not builing
	shared library.  Add gmon-start.os otherwise.
	($(objpfx)g$(start-installed-name)): Use $(objpfx)S%
	$(objpfx)gmon-start.os if builing shared library.
	($(objpfx)g$(static-start-installed-name)): Likewise.