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/bp2build/cc_prebuilt_library_static_test.go b/bp2build/cc_prebuilt_library_static_test.go
index 6116b00..17da813 100644
--- a/bp2build/cc_prebuilt_library_static_test.go
+++ b/bp2build/cc_prebuilt_library_static_test.go
@@ -39,6 +39,10 @@
 				MakeBazelTarget("cc_prebuilt_library_static", "libtest", AttrNameToString{
 					"static_library": `"libf.so"`,
 				}),
+				MakeBazelTarget("cc_prebuilt_library_static", "libtest_alwayslink", AttrNameToString{
+					"static_library": `"libf.so"`,
+					"alwayslink":     "True",
+				}),
 			},
 		})
 }
@@ -68,8 +72,14 @@
         "//build/bazel/platforms/arch:arm": "libg.so",
         "//build/bazel/platforms/arch:arm64": "libf.so",
         "//conditions:default": None,
-    })`,
-				}),
+    })`}),
+				MakeBazelTarget("cc_prebuilt_library_static", "libtest_alwayslink", AttrNameToString{
+					"alwayslink": "True",
+					"static_library": `select({
+        "//build/bazel/platforms/arch:arm": "libg.so",
+        "//build/bazel/platforms/arch:arm64": "libf.so",
+        "//conditions:default": None,
+    })`}),
 			},
 		})
 }