pngquant: Fix cross-compilation issues

packages/pngquant/configure.patch

@@ -1,6 +1,23 @@
---- ./configure	2017-11-27 20:45:47.000000000 +0530
-+++ ../configure	2017-12-02 10:42:46.176674068 +0530
-@@ -358,12 +358,6 @@
+diff -u -r ../pngquant-2.12.1/configure ./configure
+--- ../pngquant-2.12.1/configure	2018-06-04 11:30:47.000000000 +0000
++++ ./configure	2018-07-02 11:53:11.547417517 +0000
+@@ -159,10 +159,11 @@
+ 
+ find_pkgconfig() {
+     local LIBNAME=$1
+-    if pkg-config --exists "$LIBNAME" &> /dev/null; then
+-        cflags "$(pkg-config --cflags "$LIBNAME")"
+-        lflags "$(pkg-config --libs "$LIBNAME")"
+-        LIBRARY_FOUND_VERSION=$(pkg-config --modversion "$LIBNAME")
++    PKG_CONFIG=${PKG_CONFIG:pkg-config}
++    if $PKG_CONFIG --exists "$LIBNAME" &> /dev/null; then
++        cflags "$($PKG_CONFIG --cflags "$LIBNAME")"
++        lflags "$($PKG_CONFIG --libs "$LIBNAME")"
++        LIBRARY_FOUND_VERSION=$($PKG_CONFIG --modversion "$LIBNAME")
+         status "$LIBNAME" "shared ($LIBRARY_FOUND_VERSION)"
+         return 0
+     fi
+@@ -360,12 +361,6 @@
      DIRS+=("$LIQSRCDIR" "$LIQSRCDIR") # local libimagequant
  fi