cloog: update to 0.18.1 (soname bump).
glibc: depend on kernel-libc-headers; disable SSP.
gmp: bootstrap=yes.
cloog: bootstrap=yes.
isl: bootstrap=yes.
mpfr: bootstrap=yes; fix bootstrap build.
libmpc: bootstrap=yes; fix bootstrap build.
isl: fix bootstrap build.
cloog: fix bootstrap build.
binutils: enable bootstrap; disable-werror to fix build with gcc-4.9.
bzip2: rename patch to fix build.
xbps-src/build_dependencies.sh: in !CHROOT_READY case don't install pkgs with fakeroot.
xbps-src: fix bootstrap target with gcc being part of it.
gcc: sync patches with Arch; make it a bootstrap pkg and replace chroot-gcc.

- Removed --disable-bootstrap just to make sure that a proper compiler is generated.
- Adapted pkg to be part of the bootstrap process.
gcc: libgcc: replaces chroot-gcc too.
base-chroot: switch to gcc.
chroot-gcc: removed; superseded by gcc.
cloog: -devel depends on isl too.
gcc: libquadmath{,-devel} are only built natively.