Produce _alwayslink sibling targets through bp2build

Add Alwayslink to bazelPrebuiltLibraryStaticAttributes
Also adjust the corresponding tests to espect these new targets.

Test: m libc
Test: b build --config=android //prebuilts/clang/host/linux-x86:libunwind-exported_alwayslink
Test: bp2build.sh
Bug: 267214124
Change-Id: I4d996aef55321f1827947f00b0eaa52d0a14413e
diff --git a/cc/prebuilt.go b/cc/prebuilt.go
index bb517ea..5b7ba43 100644
--- a/cc/prebuilt.go
+++ b/cc/prebuilt.go
@@ -352,6 +352,7 @@
 	Static_library         bazel.LabelAttribute
 	Export_includes        bazel.StringListAttribute
 	Export_system_includes bazel.StringListAttribute
+	Alwayslink             bazel.BoolAttribute
 }
 
 // TODO(b/228623543): The below is not entirely true until the bug is fixed. For now, both targets are always generated
@@ -389,6 +390,11 @@
 
 	tags := android.ApexAvailableTags(module)
 	ctx.CreateBazelTargetModuleWithRestrictions(props, android.CommonAttributes{Name: name, Tags: tags}, attrs, prebuiltAttrs.Enabled)
+
+	_true := true
+	alwayslinkAttrs := *attrs
+	alwayslinkAttrs.Alwayslink.SetValue(&_true)
+	ctx.CreateBazelTargetModuleWithRestrictions(props, android.CommonAttributes{Name: name + "_alwayslink", Tags: tags}, &alwayslinkAttrs, prebuiltAttrs.Enabled)
 }
 
 type bazelPrebuiltLibrarySharedAttributes struct {