Config.in: disable PIC/PIE if the toolchain does not support PIE

Config.in: disable PIC/PIE if the toolchain does not support PIE

m68k does not seem to really support PIE as it raises the following
build failure with aer-inject:
/usr/lfs/hdd_v1/rc-buildroot-test/scripts/instance-1/output/host/opt/ext-toolchain/bin/../lib/gcc/m68k-buildroot-linux-uclibc/7.4.0/../../../../m68k-buildroot-linux-uclibc/bin/ld: /usr/lfs/hdd_v1/rc-buildroot-test/scripts/instance-1/output/host/m68k-buildroot-linux-uclibc/sysroot/usr/lib/Scrt1.o: in function `lib_main':
(.text+0x4): undefined reference to `__shared_flat_add_library'
/usr/lfs/hdd_v1/rc-buildroot-test/scripts/instance-1/output/host/opt/ext-toolchain/bin/../lib/gcc/m68k-buildroot-linux-uclibc/7.4.0/../../../../m68k-buildroot-linux-uclibc/bin/ld: final link failed: bad value

We also have another build failure with uclibc on microblazeel:
/home/buildroot/autobuild/instance-1/output-1/host/lib/gcc/microblazeel-buildroot-linux-uclibc/8.3.0/../../../../microblazeel-buildroot-linux-uclibc/bin/ld: final link failed: bad value
collect2: error: ld returned 1 exit status
Makefile.in:114: recipe for target '../utils/getconf' failed

So add a BR2_TOOLCHAIN_SUPPORTS_PIE dependency on BR2_PIC_PIE

Fixes:
 - http://autobuild.buildroot.net/results/4cdd6f0368cc9d3c6e88f01b1a8929eb0839b638
 - http://autobuild.buildroot.net/results/a82a484409149d7f9aff6140ddcb89f627f508c7

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Reviewed-by: Yann E. MORIN <yann.morin.1998@free.fr>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>