toolchain-external: improve sysroot rsync if ARCH_LIB_DIR != lib/lib32/lib64

toolchain-external: improve sysroot rsync if ARCH_LIB_DIR != lib/lib32/lib64

The copy_toolchain_sysroot helper in toolchain/helpers.mk performs an
rsync of various directories from the extracted external toolchain to the
corresponding directory in staging.

The relevant (simplified) snippet is:
	for i in etc $${ARCH_LIB_DIR} sbin usr usr/$${ARCH_LIB_DIR}; do \
		rsync -au --chmod=u=rwX,go=rX --exclude 'usr/lib/locale' \
			--exclude '/lib/' --exclude '/lib32/' \
			--exclude '/lib64/' \
			$${ARCH_SYSROOT_DIR}/$$i/ $(STAGING_DIR)/$$i/ ; \
	done ; \

The exclusion logic of lib/lib32/lib64 has originally been added by commit
5628776c4a4d29d0715633ea463b64cc19e19c5a with the purpose of only copying
the relevant usr/lib* directory from the toolchain to staging, instead of
all. For example, if ARCH_LIB_DIR is 'lib64', then only usr/lib64 would be
copied and usr/lib and usr/lib32 are ignored. It works by ignoring any
lib/lib32/lib64 subdirectory on the rsync of 'usr' and then separately
copying usr/{lib,lib32,lib64} as appropriate. (The exclusion rules only have
impact on the files beneath the main source directory.)

However, ARCH_LIB_DIR can take other values than (lib, lib32, lib64), for
example lib32-fp or lib64-fp (Octeon III toolchain with -march=octeon3). In
the existing code, the rsync for 'usr' would then already copy these lib
directories, and the next rsync for 'usr/$${ARCH_LIB_DIR}' does nothing.

By itself, this is not a very big problem: the staging directory simply has
some extra directories. However, a subsequent patch will create a staging
symlink from $${ARCH_LIB_DIR} to lib. The first rsync would then overwrite
that symlink with the real directory usr/$${ARCH_LIB_DIR} from the
toolchain, which is not correct.

Assuming the patch that creates the symlink ARCH_LIB_DIR->lib is applied,
the original situation after 'make clean toolchain' with an
ARCH_LIB_DIR=lib32-fp is:

$ ls -ld output/staging/{,usr/}lib* output/target/{usr/,}lib*
drwxr-xr-x 2  4096 May 26  2015 output/staging/lib
lrwxrwxrwx 1     3 Jan 20 13:47 output/staging/lib32 -> lib
lrwxrwxrwx 1     3 Jan 20 13:47 output/staging/lib32-fp -> lib
drwxr-xr-x 2  4096 Jan 20 13:47 output/staging/usr/lib
lrwxrwxrwx 1     3 Jan 20 13:47 output/staging/usr/lib32 -> lib
drwxr-xr-x 4  4096 May 26  2015 output/staging/usr/lib32-fp
drwxr-xr-x 4  4096 May 26  2015 output/staging/usr/lib64-fp
drwxr-xr-x 4  4096 May 26  2015 output/staging/usr/libexec
drwxr-xr-x 3  4096 May 26  2015 output/staging/usr/libexec32
drwxr-xr-x 3  4096 May 26  2015 output/staging/usr/libexec32-fp
drwxr-xr-x 3  4096 May 26  2015 output/staging/usr/libexec64-fp
drwxr-xr-x 2  4096 Jan 20 13:48 output/target/lib
lrwxrwxrwx 1     3 Jan 20 13:47 output/target/lib32 -> lib
lrwxrwxrwx 1     3 Jan 20 13:47 output/target/lib32-fp -> lib
drwxr-xr-x 2  4096 Jan 20 13:48 output/target/usr/lib
lrwxrwxrwx 1     3 Jan 20 13:47 output/target/usr/lib32 -> lib
lrwxrwxrwx 1     3 Jan 20 13:47 output/target/usr/lib32-fp -> lib

Notice how usr/lib32-fp is not a symlink but a directory, and the presence
of an unnecessary directory usr/lib64-fp.

This patch improves the rsync exclusion rules by excluding any lib*
directory on the first rsync. As this would also exclude any
libexec/libexec32/... directory, explicitly include them first (first match
takes precedence). This (as is already the case today) results in more
usr/libexec* directories than needed, but it is not touched by this patch.

With the fix applied, the situation becomes:

drwxr-xr-x 2 4096 May 26  2015 output/staging/lib
lrwxrwxrwx 1    3 Jan 20 14:27 output/staging/lib32 -> lib
lrwxrwxrwx 1    3 Jan 20 14:27 output/staging/lib32-fp -> lib
drwxr-xr-x 4 4096 May 26  2015 output/staging/usr/lib
lrwxrwxrwx 1    3 Jan 20 14:27 output/staging/usr/lib32 -> lib
lrwxrwxrwx 1    3 Jan 20 14:27 output/staging/usr/lib32-fp -> lib
drwxr-xr-x 4 4096 May 26  2015 output/staging/usr/libexec
drwxr-xr-x 3 4096 May 26  2015 output/staging/usr/libexec32
drwxr-xr-x 3 4096 May 26  2015 output/staging/usr/libexec32-fp
drwxr-xr-x 3 4096 May 26  2015 output/staging/usr/libexec64-fp
drwxr-xr-x 2 4096 Jan 20 14:27 output/target/lib
lrwxrwxrwx 1    3 Jan 20 14:27 output/target/lib32 -> lib
lrwxrwxrwx 1    3 Jan 20 14:27 output/target/lib32-fp -> lib
drwxr-xr-x 2 4096 Jan 20 14:27 output/target/usr/lib
lrwxrwxrwx 1    3 Jan 20 14:27 output/target/usr/lib32 -> lib
lrwxrwxrwx 1    3 Jan 20 14:27 output/target/usr/lib32-fp -> lib

For cases where ARCH_LIB_DIR is one of lib, lib32 or lib64 this fix
makes no difference, and likewise for internal toolchains.

Signed-off-by: Thomas De Schampheleire <thomas.de.schampheleire@gmail.com>
Cc: Samuel Martin <s.martin49@gmail.com>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Cc: Arnout Vandecappelle <arnout@mind.be>
Reviewed-by: Romain Naour <romain.naour@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>