fix Makefile chmod (644)
replace MD5SUM with HASH
add PKG_MIRROR_HASH when PKG_SOURCE_PROTO:=git

(PKG_SOURCE_PROTO:=svn tarballs are not reproducible for now)

Signed-off-by: Etienne Champetier <champetier.etienne@gmail.com>

We were not correctly passing down TARGET_CPPFLAGS which made external
toolchains not automatically searching for headers in $(STAGING_DIR) to
fail the build. We are also just packaging the library and headers, so
we do not need to build the tests and selftests.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>

Signed-off-by: Nicolas Thill <nico@openwrt.org>