Extract use_system_foo logic out of gyp files, patch 2

build/linux/unbundle/libxslt.gyp

Index: build/linux/unbundle/libxslt.gyp
diff --git a/build/linux/unbundle/harfbuzz.gyp b/build/linux/unbundle/libxslt.gyp
similarity index 59%
copy from build/linux/unbundle/harfbuzz.gyp
copy to build/linux/unbundle/libxslt.gyp
index 456dd384df2d5c57d9857cfb775d46ef87add2bc..f7f6bb9ab02584f13d1d76dd26b94737c5267f1a 100644
--- a/build/linux/unbundle/harfbuzz.gyp
+++ b/build/linux/unbundle/libxslt.gyp
@@ -5,22 +5,19 @@
 {
   'targets': [
     {
-      'target_name': 'harfbuzz-ng',
+      'target_name': 'libxslt',
       'type': 'none',
-      'cflags': [
-        '<!@(pkg-config --cflags harfbuzz)',
-      ],
       'direct_dependent_settings': {
         'cflags': [
-          '<!@(pkg-config --cflags harfbuzz)',
+          '<!@(pkg-config --cflags libxslt)',
         ],
       },
       'link_settings': {
         'ldflags': [
-          '<!@(pkg-config --libs-only-L --libs-only-other harfbuzz)',
+          '<!@(pkg-config --libs-only-L --libs-only-other libxslt)',
         ],
         'libraries': [
-          '<!@(pkg-config --libs-only-l harfbuzz)',
+          '<!@(pkg-config --libs-only-l libxslt)',
         ],
       },
     },