S390: Use fPIC to avoid R_390_GOT12 relocation in gcrt1.o.

if glibc is build with -march=z900 | -march=z990,
the startup file gcrt1.o (used if you link with gcc -pg)
contains R_390_GOT12 | R_390_GOT20 relocations.
Thus, an entry in the GOT can be addressed relative to the GOT pointer
with a 12 | 20 bit displacement value.
The startup files should not contain R_390_GOT12,
R_390_GOT20 relocations, but R_390_GOTENT ones.

This patch removes the overrides of pic-ccflag and
the default pic-ccflag = -fPIC in Makeconfig
is used instead to get the R_390_GOTENT relocations in gcrt1.o.

ChangeLog:

	* sysdeps/s390/s390-32/Makefile (pic-ccflag): Remove.
	* sysdeps/s390/s390-64/Makefile: Likewise.