GCC automatically detects when it is linking LTO objects, but clang does
not. Add -flto to LDFLAGS to make this work for clang too.
Signed-off-by: Allan McRae <allan@archlinux.org>
Add the 'lto' option to enable building with link time optimization
by adding '-flto' to both CFLAGS and CXXFLAGS. The 'lto' option can
be specificed both in the PKGBUILD or by setting the default in
makepkg.conf.
Signed-off-by: Allan McRae <allan@archlinux.org>