Add libc_headers header lib

This commit extracts `libc_headers` for `libasync_safe` and
`libpropertyinfoparser` (in the `system/core` repository).

Before this change, `libasync_safe` expects that `libc` is automatically
added to `system_shared_libs` of the libasync_safe vendor variant even
if `libc_defaults` explicitly declines any `system_shared_libs`.

This commit defines `libc_headers` for `libasync_safe` and
`libpropertyinfoparser` so that they can find the headers from libc
without causing circular dependencies.

Bug: 123006819
Test: make checkbuild
Change-Id: I2435ab61d36ff79ca2b4ef70bd898b795159c725
diff --git a/libc/async_safe/Android.bp b/libc/async_safe/Android.bp
index 29f90d1..a54d3b0 100644
--- a/libc/async_safe/Android.bp
+++ b/libc/async_safe/Android.bp
@@ -12,6 +12,7 @@
     recovery_available: true,
 
     include_dirs: ["bionic/libc"],
+    header_libs: ["libc_headers"],
 
     export_include_dirs: ["include"],
 }