gcc{,-bootstrap,-nogomp}: dropped dependency on ppl

The configure script does not contain any ppl option: the (eventual)
dependency on PPL will be pulled in by CLooG.

Thanks to James Russell for pointing that out.
freetype: s/freetype2/freetype/
doc: improved libgomp rule description
fontconfig: dropped --cachedir setting

This is (likely) the culprit of the issue submitted by James Russell
that resulted in the following error during "make install":

make[3]: Entering directory `/tmp/fedora-mingw-w64-fontconfig/src/fedora-mingw-w64-fontconfig-2.10.91-build-i686-w64-mingw32/src'
/usr/bin/install -c .libs/libfontconfig.dll.a /tmp/fedora-mingw-w64-fontconfig/pkg/fedora-mingw-w64-fontconfig/usr/i686-w64-mingw32/lib
 /usr/bin/mkdir -p '/tmp/fedora-mingw-w64-fontconfig/pkg/fedora-mingw-w64-fontconfig/usr/i686-w64-mingw32/lib'
 /bin/sh ../libtool   --mode=install /usr/bin/install -c libfontconfig.la '/tmp/fedora-mingw-w64-fontconfig/pkg/fedora-mingw-w64-fontconfig/usr/i686-w64-mingw32/lib'
/usr/bin/install: cannot overwrite directory ‘/tmp/fedora-mingw-w64-fontconfig/pkg/fedora-mingw-w64-fontconfig/usr/i686-w64-mingw32/lib’ with non-directory