cmd/gomobile: enable android/386, android/amd64 support

Change-Id: I044c6f773cb91b75b00171db688c6b4fbe8ec86e
Reviewed-on: https://go-review.googlesource.com/19600
Reviewed-by: David Crawshaw <crawshaw@golang.org>

cmd/gomobile/build.go

@@ -38,7 +38,10 @@ default) or ios.
 
 For -target android, if an AndroidManifest.xml is defined in the
 package directory, it is added to the APK output. Otherwise, a default
-manifest is generated.
+manifest is generated. By default, this builds a fat APK for all supported
+instruction sets (arm, 386, amd64). A subset of instruction sets can be
+selected by specifying target type with the architecture name. E.g.
+-target=android/arm,android/386.
 
 For -target ios, gomobile must be run on an OS X machine with Xcode
 installed. Support is not complete.

cmd/gomobile/doc.go

@@ -63,7 +63,7 @@ are prefixed with 'Go' unless the -prefix flag is provided.
 
 The -v flag provides verbose output, including the list of packages built.
 
-The build flags -a, -i, -n, -x, -gcflags, -ldflags, -tags, and -work
+The build flags -a, -n, -x, -gcflags, -ldflags, -tags, and -work
 are shared with the build command. For documentation, see 'go help build'.
 
 
@@ -82,7 +82,10 @@ default) or ios.
 
 For -target android, if an AndroidManifest.xml is defined in the
 package directory, it is added to the APK output. Otherwise, a default
-manifest is generated.
+manifest is generated. By default, this builds a fat APK for all supported
+instruction sets (arm, 386, amd64). A subset of instruction sets can be
+selected by specifying target type with the architecture name. E.g.
+-target=android/arm,android/386.
 
 For -target ios, gomobile must be run on an OS X machine with Xcode
 installed. Support is not complete.

cmd/gomobile/env.go

@@ -291,23 +291,21 @@ var ndk = ndkConfig{
 		toolPrefix: "arm-linux-androideabi",
 		minGoVer:   go1_5,
 	},
-	/*
-		        "386": {
-		                arch:       "x86",
-		                abi:        "x86",
-		                platform:   "android-15",
-		                gcc:        "x86-4.8",
-		                toolPrefix: "i686-linux-android",
-				minGoVer: go1_6,
 
-		        },
+	"386": {
-		        "amd64": {
+		arch:       "x86",
-		                arch:       "x86_64",
+		abi:        "x86",
-		                abi:        "x86_64",
+		platform:   "android-15",
-		                platform:   "android-21",
+		gcc:        "x86-4.8",
-		                gcc:        "x86_64-4.9",
+		toolPrefix: "i686-linux-android",
-		                toolPrefix: "x86_64-linux-android",
+		minGoVer:   go1_6,
-				minGoVer: go1_6,
+	},
-		        },
+	"amd64": {
-	*/
+		arch:       "x86_64",
+		abi:        "x86_64",
+		platform:   "android-21",
+		gcc:        "x86_64-4.9",
+		toolPrefix: "x86_64-linux-android",
+		minGoVer:   go1_6,
+	},
 }