Apply upstream change from libffi to check for HAVE_AS_X86_PCREL for all
x86 targets. This should eliminate any text relocations, in particular
for the i386 build, making it possible to build the port with lld
without having to use -z notext.

Obtained from: https://github.com/libffi/libffi/pull/174
Approved by: zeising (maintainer)
PR: 214864
MFH: 2017Q4