builder: more minor mingw cross fixes

Do not defer evaluating build env variables in mingw-cross.sh, this
interferes with switching them between host/target.

In build_dist() adjust the LDFLAGS and LIBS after pre_build has run,
because host/target env setting happens in pre_build and adjustments get
lost.

tools/builder/core.sh

@@ -1336,6 +1336,9 @@ build_dist() {
 
     puts "${NL}Building $current_dist${NL}${NL}"
 
+    dist_patch "$current_dist"
+    dist_pre_build "$current_dist"
+
     ORIG_LDFLAGS=$LDFLAGS
     ORIG_LIBS=$LIBS
 
@@ -1348,9 +1351,6 @@ build_dist() {
     export LDFLAGS="$LDFLAGS $(eval puts "$(dist_extra_ldflags "$current_dist")")"
     export LIBS="$LIBS $(eval puts "$(dist_extra_libs "$current_dist")")"
 
-    dist_patch "$current_dist"
-    dist_pre_build "$current_dist"
-
     configure_override=$(dist_configure_override "$current_dist")
     install_override=$(dist_install_override "$current_dist")
     build_override=$(dist_build_override "$current_dist")

tools/builder/mingw-cross.sh

@@ -46,11 +46,11 @@ export CC='${target_arch}-gcc'
 export CXX='${target_arch}-g++'
 export STRIP='${target_arch}-strip'
 
-export CPPFLAGS="\$CPPFLAGS"
-export CFLAGS="\$CFLAGS\${CFLAGS:+ }-L/usr/${target_arch}/usr/lib${lib_suffix}"
-export CXXFLAGS="\$CXXFLAGS\${CXXFLAGS:+ }-L/usr/${target_arch}/usr/lib${lib_suffix}"
-export OBJCXXFLAGS="\$OBJCXXFLAGS\${OBJCXXFLAGS:+ }-L/usr/${target_arch}/usr/lib${lib_suffix}"
-export LDFLAGS="-L/usr/${target_arch}/usr/lib${lib_suffix} \$LDFLAGS"
+export CPPFLAGS="$CPPFLAGS"
+export CFLAGS="$CFLAGS${CFLAGS:+ }-L/usr/${target_arch}/usr/lib${lib_suffix}"
+export CXXFLAGS="$CXXFLAGS${CXXFLAGS:+ }-L/usr/${target_arch}/usr/lib${lib_suffix}"
+export OBJCXXFLAGS="$OBJCXXFLAGS${OBJCXXFLAGS:+ }-L/usr/${target_arch}/usr/lib${lib_suffix}"
+export LDFLAGS="-L/usr/${target_arch}/usr/lib${lib_suffix} $LDFLAGS"
 
 EOF
 )