Enable use_custom_libcxx on Linux

chromiumcontent/args/ffmpeg.gn

@@ -7,8 +7,10 @@ proprietary_codecs = false
 is_component_ffmpeg = true
 ffmpeg_branding = "Chromium"
 
-# Always use the system provided standard library
-use_custom_libcxx = false
+# Use the system provided standard library on platforms other than Linux.
+if (target_os != "linux") {
+  use_custom_libcxx = false
+}
 
 # Jumbo build should improve compilation times.
 # https://chromium.googlesource.com/chromium/src/+/master/docs/jumbo.md

chromiumcontent/args/shared_library.gn

@@ -10,8 +10,10 @@ proprietary_codecs = true
 is_component_ffmpeg = true
 ffmpeg_branding = "Chrome"
 
-# Always use the system provided standard library
-use_custom_libcxx = false
+# Use the system provided standard library on platforms other than Linux.
+if (target_os != "linux") {
+  use_custom_libcxx = false
+}
 
 # Jumbo build should improve compilation times.
 # https://chromium.googlesource.com/chromium/src/+/master/docs/jumbo.md

chromiumcontent/args/static_library.gn

@@ -14,8 +14,10 @@ ffmpeg_branding = "Chrome"
 # scenario
 is_cfi = false
 
-# Always use the system provided standard library
-use_custom_libcxx = false
+# Use the system provided standard library on platforms other than Linux.
+if (target_os != "linux") {
+  use_custom_libcxx = false
+}
 
 # Jumbo build should improve compilation times.
 # https://chromium.googlesource.com/chromium/src/+/master/docs/jumbo.md