Support tailoring clang --target flag based on min sdk version.

Bug: 215748260
Test: Tested using aquery to verify the --target flag; add added unit

Change-Id: Ifb13509db7d1e110316aa44d55ec9cccaa4b83d1
diff --git a/bp2build/cc_library_shared_conversion_test.go b/bp2build/cc_library_shared_conversion_test.go
index 78192fe..22c9dfe 100644
--- a/bp2build/cc_library_shared_conversion_test.go
+++ b/bp2build/cc_library_shared_conversion_test.go
@@ -136,6 +136,8 @@
         "header_lib_1",
         "header_lib_2"
     ],
+    sdk_version: "current",
+    min_sdk_version: "29",
 
     // TODO: Also support export_header_lib_headers
 }`,
@@ -174,6 +176,8 @@
         ":whole_static_lib_1",
         ":whole_static_lib_2",
     ]`,
+        "sdk_version": `"current"`,
+        "min_sdk_version": `"29"`,
 			}),
 		},
 	})