Rework how use_system_harfbuzz works a bit.

build/linux/system.gyp

Index: build/linux/system.gyp
diff --git a/build/linux/system.gyp b/build/linux/system.gyp
index a325acac044f2b2458bbcc332a5231b713c13266..db29cff6ac5edfd3cacb1dfd504e754c32e19deb 100644
--- a/build/linux/system.gyp
+++ b/build/linux/system.gyp
@@ -1190,29 +1190,29 @@
             ['_toolset=="target"', {
               'direct_dependent_settings': {
                 'cflags': [
-                  '<!@(<(pkg-config) --cflags pangocairo pangoft2)',
+                  '<!@(<(pkg-config) --cflags pangocairo)',
                 ],
               },
               'link_settings': {
                 'ldflags': [
-                  '<!@(<(pkg-config) --libs-only-L --libs-only-other pangocairo pangoft2)',
+                  '<!@(<(pkg-config) --libs-only-L --libs-only-other pangocairo)',
                 ],
                 'libraries': [
-                  '<!@(<(pkg-config) --libs-only-l pangocairo pangoft2)',
+                  '<!@(<(pkg-config) --libs-only-l pangocairo)',
                 ],
               },
             }, {
               'direct_dependent_settings': {
                 'cflags': [
-                  '<!@(<(pkg-config) --cflags pangocairo pangoft2)',
+                  '<!@(<(pkg-config) --cflags pangocairo)',
                 ],
               },
               'link_settings': {
                 'ldflags': [
-                  '<!@(<(pkg-config) --libs-only-L --libs-only-other pangocairo pangoft2)',
+                  '<!@(<(pkg-config) --libs-only-L --libs-only-other pangocairo)',
                 ],
                 'libraries': [
-                  '<!@(<(pkg-config) --libs-only-l pangocairo pangoft2)',
+                  '<!@(<(pkg-config) --libs-only-l pangocairo)',
                 ],
               },
             }],