make.sh: Pass BUILD_PLATFORM variable to build environment

Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>

tools/make-functions

@@ -514,6 +514,7 @@ enterchroot() {
 		BUILDTARGET="${BUILDTARGET}" \
 		CROSSTARGET="${CROSSTARGET}" \
 		BUILD_ARCH="${BUILD_ARCH}" \
+		BUILD_PLATFORM="${BUILD_PLATFORM}" \
 		CCACHE_DIR=/usr/src/ccache \
 		CCACHE_COMPRESS="${CCACHE_COMPRESS}" \
 		CCACHE_COMPILERCHECK="${CCACHE_COMPILERCHECK}" \