Use correct linker flags for iOS release builds.
Use correct linker flags for iOS release builds.

iOS uses the same linker as Mac and thus should use the same linker flags
in Release mode (is_debug=false).

Fix the following error when linking base_unittest in Release mode:

FAILED: ../../third_party/llvm-build/Release+Asserts/bin/clang++ -arch x86_64 -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator9.0.sdk -stdlib=libc++ -mios-simulator-version-min=7.0 -Wl,-O1 -Wl,--gc-sections -Wl,--as-needed -o ./base_unittests.app/base_unittests -Wl,-filelist,./base_unittests.app/base_unittests.rsp  -framework UIKit -framework QuartzCore -framework OpenGLES -framework CoreFoundation -framework CoreGraphics -framework CoreText -framework Foundation
ld: unknown option: -O1

BUG=459705

Review URL: https://codereview.chromium.org/1274633004

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#342523}

ltilve/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend