configure.sh: quote local variables

fixes issue #711

specifying a multiword CC, e.g., CC='gcc -m32', would cause the failure
under dash

reported in
https://bugs.gentoo.org/show_bug.cgi?id=498136

patch by floppymaster at gmail dot com

Change-Id: I2ba246f765646161538622739961ec0f6c2d8c2d

build/make/configure.sh

@@ -405,8 +405,8 @@ true
 }
 
 write_common_target_config_mk() {
-    local CC=${CC}
-    local CXX=${CXX}
+    local CC="${CC}"
+    local CXX="${CXX}"
     enabled ccache && CC="ccache ${CC}"
     enabled ccache && CXX="ccache ${CXX}"
     print_webm_license $1 "##" ""