Stop manually setting CC/AR/RANLIB when building autotools projects

Since we have triplet prefixed wrappers for all tools, and wrappers
named <triplet>-gcc/g++ as well, we don't need to manually provide
them.

build-mingw-w64-libraries.sh

@@ -22,8 +22,7 @@ for lib in winpthreads winstorecompat; do
     for arch in $ARCHS; do
         mkdir -p build-$arch
         cd build-$arch
-        ../configure --host=$arch-w64-mingw32 --prefix=$PREFIX/$arch-w64-mingw32 \
-            CC=$arch-w64-mingw32-clang AR=llvm-ar RANLIB=llvm-ranlib
+        ../configure --host=$arch-w64-mingw32 --prefix=$PREFIX/$arch-w64-mingw32
         make -j$CORES
         make install
         cd ..

build-mingw-w64.sh

@@ -101,8 +101,7 @@ if [ -z "$HOST" ]; then
             ;;
         esac
         FLAGS="$FLAGS --with-default-msvcrt=$DEFAULT_MSVCRT"
-        ../configure --host=$arch-w64-mingw32 --prefix=$PREFIX/$arch-w64-mingw32 $FLAGS \
-            CC=$arch-w64-mingw32-clang AR=llvm-ar RANLIB=llvm-ranlib DLLTOOL=llvm-dlltool
+        ../configure --host=$arch-w64-mingw32 --prefix=$PREFIX/$arch-w64-mingw32 $FLAGS
         make -j$CORES
         make install
         cd ..