Add RPATH to shared libraries

Fixes libfontconfig.so not being able to find libfreetype_harfbuzz.so:

$ ldd libfontconfig.so | grep freetype_harfbuzz
	libfreetype_harfbuzz.so => not found
$ ls libfreetype_harfbuzz.so
libfreetype_harfbuzz.so

R=thakis

Bug: 911836,912366
Change-Id: Ia0aaed8fc2c745b02cecf9ee3ce9888c1d8ccf77
Reviewed-on: https://chromium-review.googlesource.com/c/1362457
Commit-Queue: Thomas Anderson <thomasanderson@chromium.org>
Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Cr-Commit-Position: refs/heads/master@{#614255}

build/config/BUILD.gn

@@ -385,6 +385,8 @@ config("shared_library_config") {
     configs += [ "//build/config/ios:ios_dynamic_flags" ]
   } else if (is_chromecast) {
     configs += [ "//build/config/chromecast:shared_library_config" ]
+  } else if (is_linux || current_os == "aix") {
+    configs += [ "//build/config/gcc:shared_library_config" ]
   }
 
   # If we're using the prebuilt instrumented libraries with the sanitizers, we

build/config/gcc/BUILD.gn

@@ -84,20 +84,24 @@ config("rpath_for_built_shared_libraries") {
   }
 }
 
+if (is_component_build && !is_android) {
+  # See the rpath_for... config above for why this is necessary for component
+  # builds.
+  executable_and_shared_library_configs_ =
+      [ ":rpath_for_built_shared_libraries" ]
+} else {
+  executable_and_shared_library_configs_ = []
+}
+
 # Settings for executables.
 config("executable_config") {
+  configs = executable_and_shared_library_configs_
   ldflags = [ "-pie" ]
   if (is_android) {
     ldflags += [
       "-Bdynamic",
       "-Wl,-z,nocopyreloc",
     ]
-  } else {
-    # See the rpath_for... config above for why this is necessary for component
-    # builds.
-    if (is_component_build) {
-      configs = [ ":rpath_for_built_shared_libraries" ]
-    }
   }
 
   if (!is_android && current_os != "aix") {
@@ -116,3 +120,8 @@ config("executable_config") {
     ]
   }
 }
+
+# Settings for shared libraries.
+config("shared_library_config") {
+  configs = executable_and_shared_library_configs_
+}