Move localtime.c over to CachedProperty.

Since localtime.c is C, this entails pulling our code out into its own
C++ file, which we should probably have done years ago anyway.

Bug: N/A
Test: ran tests, and manually tested via Settings
Change-Id: Ifc787a553e8f739a87641a2d35321aca40a47286
diff --git a/libc/Android.bp b/libc/Android.bp
index 8c6f596..7c137b0 100644
--- a/libc/Android.bp
+++ b/libc/Android.bp
@@ -129,6 +129,7 @@
     defaults: ["libc_defaults"],
     srcs: [
         "tzcode/**/*.c",
+        "tzcode/bionic.cpp",
         "upstream-openbsd/lib/libc/time/wcsftime.c", // tzcode doesn't include wcsftime, so we use the OpenBSD one.
     ],