Use -Werror in system/core

* Move -Wall -Werror from cppflags to cflags.
* Fix/suppress warning on unused variables.

Bug: 66996870
Test: build with WITH_TIDY=1
Change-Id: I1e05e96a1d0bcb2ccef1ce456504b3af57167cc5
diff --git a/libprocinfo/Android.bp b/libprocinfo/Android.bp
index b568ee5..1cfabd5 100644
--- a/libprocinfo/Android.bp
+++ b/libprocinfo/Android.bp
@@ -14,14 +14,14 @@
 // limitations under the License.
 //
 
-libprocinfo_cppflags = [
-    "-Wall",
-    "-Wextra",
-    "-Werror",
-]
+cc_defaults {
+    name: "libprocinfo_defaults",
+    cflags: ["-Wall", "-Werror", "-Wextra"],
+}
 
 cc_library {
     name: "libprocinfo",
+    defaults: ["libprocinfo_defaults"],
     vendor_available: true,
     vndk: {
         enabled: true,
@@ -30,7 +30,6 @@
     srcs: [
         "process.cpp",
     ],
-    cppflags: libprocinfo_cppflags,
 
     local_include_dirs: ["include"],
     export_include_dirs: ["include"],
@@ -52,6 +51,7 @@
 // ------------------------------------------------------------------------------
 cc_test {
     name: "libprocinfo_test",
+    defaults: ["libprocinfo_defaults"],
     host_supported: true,
     srcs: [
         "process_test.cpp",
@@ -65,7 +65,6 @@
         },
     },
 
-    cppflags: libprocinfo_cppflags,
     shared_libs: ["libbase", "libprocinfo"],
 
     compile_multilib: "both",