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/arm_device.go

@@ -237,6 +237,7 @@ var (
 )
 
 type toolchainArm struct {
+	toolchainBionic
 	toolchain32Bit
 	ldflags              string
 	lldflags             string