build-mingw-w64: Pass --disable-dependency-tracking when configuring mingw-w64-crt on MSYS2

Configuring the mingw-w64-crt build takes a really long time on MSYS2;
the generating Makefile phase takes easily 4-5 minutes, when the rest
of configure runs in a matter of seconds. By passing
--disable-dependency-tracking, the whole configure for mingw-w64-crt
takes 11-14 seconds where it previously took many mnutes.

This comes with the drawback that these build directories aren't
suitable for incremental development (unless manual care is taken
to rebuild all necessary files), but these builds are mostly done
for non-interactive building.

Thanks to Jeremy Drake for realizing this optimization opportunity,
and LIU Hao for making me aware of it.

build-mingw-w64.sh

@@ -74,6 +74,12 @@ if command -v gmake >/dev/null; then
     MAKE=gmake
 fi
 
+case $(uname) in
+MINGW*|MSYS*)
+    CRT_CONFIG_FLAGS="--disable-dependency-tracking"
+    ;;
+esac
+
 export PATH="$PREFIX/bin:$PATH"
 
 unset CC
@@ -126,7 +132,7 @@ for arch in $ARCHS; do
         ;;
     esac
     FLAGS="$FLAGS --with-default-msvcrt=$DEFAULT_MSVCRT"
-    ../configure --host=$arch-w64-mingw32 --prefix="$PREFIX/$arch-w64-mingw32" $FLAGS $CFGUARD_FLAGS
+    ../configure --host=$arch-w64-mingw32 --prefix="$PREFIX/$arch-w64-mingw32" $FLAGS $CFGUARD_FLAGS $CRT_CONFIG_FLAGS
     $MAKE -j$CORES
     $MAKE install
     cd ..