don't pollute cross-compilation environment with host pkg-config

Change-Id: I37a9a801c6bc885bdc5e0cbb9cd4ed527095acf8
Reviewed-on: https://gerrit.libreoffice.org/21587Reviewed-by: Tor Lillqvist <tml@collabora.com>
Tested-by: Tor Lillqvist <tml@collabora.com>

configure.ac

@@ -490,6 +490,7 @@ if test -n "$with_android_ndk"; then
     ANDROIDCFLAGS="$ANDROIDCFLAGS -ffunction-sections -fdata-sections"
     ANDROIDCFLAGS="$ANDROIDCFLAGS -L$ANDROID_NDK_HOME/sources/cxx-stl/gnu-libstdc++/${ANDROID_NDK_TOOLCHAIN_VERSION_SUBDIR}libs/$ANDROID_APP_ABI"
     ANDROIDCFLAGS="$ANDROIDCFLAGS --sysroot=$ANDROID_NDK_HOME/platforms/android-${ANDROID_API_LEVEL}/arch-${ANDROID_ARCH}"
+    export PKG_CONFIG_LIBDIR="$ANDROID_BINUTILS_PREBUILT_ROOT/lib/pkgconfig"
 
     if test -n "$ANDROID_USING_CLANG"; then
         ANDROIDCFLAGS="$ANDROIDCFLAGS -Qunused-arguments"
@@ -4626,7 +4627,7 @@ if test "$cross_compiling" = "yes"; then
     unset CC CXX SYSBASE CFLAGS
     unset AR NM OBJDUMP PKG_CONFIG RANLIB READELF STRIP
     unset CPPUNIT_CFLAGS CPPUNIT_LIBS
-    unset LIBXML_CFLAGS LIBXML_LIBS LIBXSLT_CFLAGS LIBXSLT_LIBS XSLTPROC
+    unset LIBXML_CFLAGS LIBXML_LIBS LIBXSLT_CFLAGS LIBXSLT_LIBS XSLTPROC PKG_CONFIG_LIBDIR
     test -n "$CC_FOR_BUILD" && export CC="$CC_FOR_BUILD"
     test -n "$CXX_FOR_BUILD" && export CXX="$CXX_FOR_BUILD"
     test -n "$PKG_CONFIG_FOR_BUILD" && export PKG_CONFIG="$PKG_CONFIG_FOR_BUILD"