Create toolchainBionic for the various bionic-based toolchains to inherit from

Host bionic and each of the device bionic architectures will share some
new toolchain functionality in common, create a toolchainBionic and embed
it into the toolchains.  Use it to implement Bionic() once and change
the default implementation from true to false.

Test: go test ./cc/...
Test: m checkbuild
Change-Id: Ia34b80d9691edc4ab1cbdbd005d1ffc950d0881c

cc/config/x86_device.go

@@ -134,6 +134,7 @@ func init() {
 }
 
 type toolchainX86 struct {
+	toolchainBionic
 	toolchain32Bit
 	toolchainClangCflags string
 }