GN: add 32-bit and Release iOS builders.

And roll recipes to the point where they pass target_cpu to GN,
adding x86_64 as an alias for x64.

CQ_INCLUDE_TRYBOTS=skia.primary:Build-Mac-Clang-arm64-Debug-GN_iOS,Build-Mac-Clang-arm64-Release-GN_iOS,Build-Mac-Clang-arm-Debug-GN_iOS,Build-Mac-Clang-arm-Release-GN_iOS

Change-Id: I1933d5803ec7f59f78576c5a7b16489362905a97
Reviewed-on: https://skia-review.googlesource.com/7403
Reviewed-by: Eric Boren <borenet@google.com>
Commit-Queue: Mike Klein <mtklein@chromium.org>
diff --git a/infra/bots/gen_tasks.go b/infra/bots/gen_tasks.go
index 89a6fe2..5fc6a32 100644
--- a/infra/bots/gen_tasks.go
+++ b/infra/bots/gen_tasks.go
@@ -40,8 +40,11 @@
 	JOBS = []string{
 		"Build-Mac-Clang-Arm7-Debug-iOS",
 		"Build-Mac-Clang-Arm7-Release-iOS",
+		"Build-Mac-Clang-arm-Debug-GN_iOS",
+		"Build-Mac-Clang-arm-Release-GN_iOS",
 		"Build-Mac-Clang-arm64-Debug-Android",
 		"Build-Mac-Clang-arm64-Debug-GN_iOS",
+		"Build-Mac-Clang-arm64-Release-GN_iOS",
 		"Build-Mac-Clang-x86_64-Debug",
 		"Build-Mac-Clang-x86_64-Debug-CommandBuffer",
 		"Build-Mac-Clang-x86_64-Release",