Properly handle --disable-default-pie [BZ #28780]

When --disable-default-pie is used, all glibc programs and the testsuite
should be built as position dependent executables (non-PIE), regardless
if the build compiler supports PIE or static PIE.

When --disable-default-pie is used, don't build static PIE by default.

This fixes BZ #28780.

Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>