bp2build: Handle target.linux

Also refactor target.bionic to be handled not as its own configuration
axis, but instead to be grouped into os selects handling.

This allows us to remove libbase and its dependencies from the bp2build
denylist.

Test: mixed_droid.sh CI
Change-Id: I92f30074d286306207653fe37589835ae3db16c4

bazel/configurability.go

@@ -91,11 +91,6 @@ var (
 		ConditionsDefaultConfigKey: ConditionsDefaultSelectKey, // The default condition of an os select map.
 	}
 
-	platformBionicMap = map[string]string{
-		"bionic":                   "//build/bazel/platforms/os:bionic",
-		ConditionsDefaultConfigKey: ConditionsDefaultSelectKey, // The default condition of an os select map.
-	}
-
 	platformOsArchMap = map[string]string{
 		osArchAndroidArm:           "//build/bazel/platforms/os_arch:android_arm",
 		osArchAndroidArm64:         "//build/bazel/platforms/os_arch:android_arm64",
@@ -122,7 +117,6 @@ const (
 	arch
 	os
 	osArch
-	bionic
 	productVariables
 )
 
@@ -132,7 +126,6 @@ func (ct configurationType) String() string {
 		arch:             "arch",
 		os:               "os",
 		osArch:           "arch_os",
-		bionic:           "bionic",
 		productVariables: "product_variables",
 	}[ct]
 }
@@ -155,10 +148,6 @@ func (ct configurationType) validateConfig(config string) {
 		if _, ok := platformOsArchMap[config]; !ok {
 			panic(fmt.Errorf("Unknown os+arch: %s", config))
 		}
-	case bionic:
-		if _, ok := platformBionicMap[config]; !ok {
-			panic(fmt.Errorf("Unknown for %s: %s", ct.String(), config))
-		}
 	case productVariables:
 		// do nothing
 	default:
@@ -178,8 +167,6 @@ func (ct configurationType) SelectKey(config string) string {
 		return platformOsMap[config]
 	case osArch:
 		return platformOsArchMap[config]
-	case bionic:
-		return platformBionicMap[config]
 	case productVariables:
 		if config == ConditionsDefaultConfigKey {
 			return ConditionsDefaultSelectKey
@@ -199,8 +186,6 @@ var (
 	OsConfigurationAxis = ConfigurationAxis{configurationType: os}
 	// An axis for arch+os-specific configurations
 	OsArchConfigurationAxis = ConfigurationAxis{configurationType: osArch}
-	// An axis for bionic os-specific configurations
-	BionicConfigurationAxis = ConfigurationAxis{configurationType: bionic}
 )
 
 // ProductVariableConfigurationAxis returns an axis for the given product variable