Toolchain: Use "install.sh" to install LibC and LibM.

Toolchain/BuildIt.sh

@@ -93,8 +93,8 @@ pushd "$DIR/Build/"
         make install-gcc install-target-libgcc || exit 1
 
         echo "XXX serenity libc and libm"
-        make -C "$DIR/../Libraries/LibC/" install
-        make -C "$DIR/../Libraries/LibM/" install
+        ( cd "$DIR/../Libraries/LibC/" && ./install.sh )
+        ( cd "$DIR/../Libraries/LibM/" && ./install.sh )
 
         echo "XXX build libstdc++"
         make all-target-libstdc++-v3 || exit 1