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_linux_host.go

@@ -245,10 +245,6 @@ func (t *toolchainLinux) AvailableLibraries() []string {
 	return linuxAvailableLibraries
 }
 
-func (t *toolchainLinux) Bionic() bool {
-	return false
-}
-
 var toolchainLinuxX86Singleton Toolchain = &toolchainLinuxX86{}
 var toolchainLinuxX8664Singleton Toolchain = &toolchainLinuxX8664{}