Allow remote execution of link actions.

This CL adds a remoteexec package that allows adding a configurable RBE
prefix to the template.

Test: built aosp crosshatch userdebug with and without RBE_CXX_LINKS.
Change-Id: Ica920c3d7f79f2996210b9cbd448126451c1707c

Android.bp

@@ -132,6 +132,7 @@ bootstrap_go_package {
     pkgPath: "android/soong/cc/config",
     deps: [
         "soong-android",
+        "soong-remoteexec",
     ],
     srcs: [
         "cc/config/clang.go",
@@ -547,6 +548,22 @@ bootstrap_go_package {
     pluginFor: ["soong_build"],
 }
 
+bootstrap_go_package {
+    name: "soong-remoteexec",
+    pkgPath: "android/soong/remoteexec",
+    deps: [
+        "blueprint",
+        "soong-android",
+    ],
+    srcs: [
+        "remoteexec/remoteexec.go",
+    ],
+    testSrcs: [
+        "remoteexec/remoteexec_test.go",
+    ],
+    pluginFor: ["soong_build"],
+}
+
 //
 // Defaults to enable various configurations of host bionic
 //