Add musl defaults in bp2build

Bug: 261657184
Test: Unit Tests
Test: Manual Inspection of generated files
Change-Id: I69864abb410fddecd530fc75f2531aff33b33c97
diff --git a/bp2build/cc_library_conversion_test.go b/bp2build/cc_library_conversion_test.go
index f924d00..052bc32 100644
--- a/bp2build/cc_library_conversion_test.go
+++ b/bp2build/cc_library_conversion_test.go
@@ -1806,6 +1806,11 @@
 		ModuleTypeUnderTestFactory: cc.LibraryFactory,
 		Blueprint: soongCcLibraryPreamble + `
 cc_library {
+	name: "libc_musl",
+	bazel_module: { bp2build_available: false },
+}
+
+cc_library {
     name: "target_linux_bionic_empty",
     target: {
         linux_bionic: {
@@ -1816,7 +1821,10 @@
 }
 `,
 		ExpectedBazelTargets: makeCcLibraryTargets("target_linux_bionic_empty", AttrNameToString{
-			"system_dynamic_deps": `[]`,
+			"system_dynamic_deps": `select({
+        "//build/bazel/platforms/os:linux_musl": [":libc_musl"],
+        "//conditions:default": [],
+    })`,
 		}),
 	},
 	)
@@ -1829,6 +1837,11 @@
 		ModuleTypeUnderTestFactory: cc.LibraryFactory,
 		Blueprint: soongCcLibraryPreamble + `
 cc_library {
+	name: "libc_musl",
+	bazel_module: { bp2build_available: false },
+}
+
+cc_library {
     name: "target_bionic_empty",
     target: {
         bionic: {
@@ -1839,12 +1852,68 @@
 }
 `,
 		ExpectedBazelTargets: makeCcLibraryTargets("target_bionic_empty", AttrNameToString{
-			"system_dynamic_deps": `[]`,
+			"system_dynamic_deps": `select({
+        "//build/bazel/platforms/os:linux_musl": [":libc_musl"],
+        "//conditions:default": [],
+    })`,
 		}),
 	},
 	)
 }
 
+func TestCcLibrary_SystemSharedLibsMuslEmpty(t *testing.T) {
+	runCcLibraryTestCase(t, Bp2buildTestCase{
+		Description:                "cc_library system_shared_lib empty for musl variant",
+		ModuleTypeUnderTest:        "cc_library",
+		ModuleTypeUnderTestFactory: cc.LibraryFactory,
+		Blueprint: soongCcLibraryPreamble + `
+cc_library {
+		name: "libc_musl",
+		bazel_module: { bp2build_available: false },
+}
+
+cc_library {
+    name: "target_musl_empty",
+    target: {
+        musl: {
+            system_shared_libs: [],
+        },
+    },
+    include_build_directory: false,
+}
+`,
+		ExpectedBazelTargets: makeCcLibraryTargets("target_musl_empty", AttrNameToString{
+			"system_dynamic_deps": `[]`,
+		}),
+	})
+}
+
+func TestCcLibrary_SystemSharedLibsLinuxMuslEmpty(t *testing.T) {
+	runCcLibraryTestCase(t, Bp2buildTestCase{
+		Description:                "cc_library system_shared_lib empty for linux_musl variant",
+		ModuleTypeUnderTest:        "cc_library",
+		ModuleTypeUnderTestFactory: cc.LibraryFactory,
+		Blueprint: soongCcLibraryPreamble + `
+cc_library {
+		name: "libc_musl",
+		bazel_module: { bp2build_available: false },
+}
+
+cc_library {
+    name: "target_linux_musl_empty",
+    target: {
+        linux_musl: {
+            system_shared_libs: [],
+        },
+    },
+    include_build_directory: false,
+}
+`,
+		ExpectedBazelTargets: makeCcLibraryTargets("target_linux_musl_empty", AttrNameToString{
+			"system_dynamic_deps": `[]`,
+		}),
+	})
+}
 func TestCcLibrary_SystemSharedLibsSharedAndRoot(t *testing.T) {
 	runCcLibraryTestCase(t, Bp2buildTestCase{
 		Description:                "cc_library system_shared_libs set for shared and root",