Fix Android and Emscripten compilation issues

These were introduced with some of the changes required for proper Linux
cross-compilation support.

Author: livecodefraser

libfreetype/libfreetype.gyp

@@ -10,6 +10,8 @@
 			'target_name': 'libfreetype',
 			'type': 'static_library',
 
+			'toolsets': ['target', 'host'],
+
 			'variables':
 			{
 				'silence_warnings': 1,
@@ -167,11 +169,11 @@
 				],
 			},
 
-			'conditions':
+			'target_conditions':
 			[
-				# This library is only required on Android
+				# This library is only required on Emscripten and Android
 				[
-                                        'OS != "android" and OS != "emscripten"',
+					'toolset_os not in ("emscripten", "android")',
 					{
 						'type': 'none',
 					},

libharfbuzz/libharfbuzz.gyp

@@ -10,6 +10,8 @@
 			'target_name': 'libharfbuzz',
 			'type': 'static_library',
 
+			'toolsets': ['target', 'host'],
+
 			'variables':
 			{
 				'silence_warnings': 1,
@@ -78,6 +80,17 @@
 					'../../prebuilt/include',
 				],
 			},
+
+			'target_conditions':
+			[
+				# This library is only required on Emscripten and Android
+				[
+					'toolset_os not in ("emscripten", "android")',
+					{
+						'type': 'none',
+					},
+				],
+			],
 		},
 	],
 }

libskia/libskia.gyp

@@ -1701,6 +1701,19 @@
 				['exclude', '/xps/'],
 			],
 
+			'conditions':
+			[
+				[
+					'OS in ("emscripten", "android")',
+					{
+						'dependencies':
+						[
+							'../libfreetype/libfreetype.gyp:libfreetype',
+						],
+					}
+				],
+			],
+
 			'target_conditions':
 			[
 				[
@@ -1837,12 +1850,6 @@
                             'SK_FONT_FILE_PREFIX="/boot/standalone/"',
                         ],
 
-                        'dependencies':
-                        [
-                            '../libexpat/libexpat.gyp:libexpat',
-                            '../libfreetype/libfreetype.gyp:libfreetype',
-                        ],
-
                         'sources!':
 						[
                             'src/ports/SkDebug_stdio.cpp',
@@ -1901,22 +1908,21 @@
 				[
 					'toolset_os == "android"',
 					{
-						'dependencies':
-						[
-							'../libexpat/libexpat.gyp:libexpat',
-							'../libfreetype/libfreetype.gyp:libfreetype',
-						],
-
 						'defines':
 						[
                             'SK_BUILD_FOR_ANDROID',
                             'SK_BUILD_FOR_ANDROID_NDK',
 						],
 
                         # Need to include the cpufeatures module from the Android NDK
+						'variables':
+						{
+							# Default value because only Android defines the <(android_ndk_path) variable.
+							'android_ndk_path%': '',
+						},
                         'include_dirs':
                         [
-                            '>(android_ndk_path)/sources/android/cpufeatures',
+                            '<(android_ndk_path)/sources/android/cpufeatures',
                         ],
                         'sources':
                         [