add target_compatible_with stanza for host targets

Soong modules that are specific for the host platform (e.g.
java_library_host, cc_binary_host, java_genrule_host, etc.) should
not be built on the target platform (Android), so we add a
target_compatible_with attribute to skip this type of module on an
Android target build.

Bug: 215229742
Test: go test ./bp2build
Change-Id: Ifb76ef4e0dc4cb3adb6a64b5c375ce36f7973e48

bp2build/java_library_host_conversion_test.go

@@ -48,9 +48,17 @@ java_library_host {
 			makeBazelTarget("java_library", "java-lib-host-1", attrNameToString{
 				"srcs": `["a.java"]`,
 				"deps": `[":java-lib-host-2"]`,
+				"target_compatible_with": `select({
+        "//build/bazel/platforms/os:android": ["@platforms//:incompatible"],
+        "//conditions:default": [],
+    })`,
 			}),
 			makeBazelTarget("java_library", "java-lib-host-2", attrNameToString{
 				"srcs": `["c.java"]`,
+				"target_compatible_with": `select({
+        "//build/bazel/platforms/os:android": ["@platforms//:incompatible"],
+        "//conditions:default": [],
+    })`,
 			}),
 		},
 	})