llvm: use gcc for compilation

This fixes building llvm-32 after a bump of llvm (and thus clang breaking
until a rebuild).

llvm/Pkgfile

@@ -11,6 +11,9 @@ source=(http://llvm.org/releases/$version/$name-$version.src.tar.xz \
         config.h llvm-config.h)
 
 build() {
+  export CC=gcc
+  export CXX=g++
+
   cd $name-$version.src
 
   mkdir build