Add bionic/libc/include to exported_include_dirs

This commit adds "include" (full path: "bionic/libc/include") to
exported_include_dirs for libc.  Without this change,
header-abi-checker will strip all functions from ABI dumps.

Bug: 117963950
Test: libc.so.lsdump has a non-empty functions array
Change-Id: I192a4ec0251f1320ced56c6201818076ebd2a2da
diff --git a/libc/Android.bp b/libc/Android.bp
index 681394f..2ba4f78 100644
--- a/libc/Android.bp
+++ b/libc/Android.bp
@@ -1702,6 +1702,7 @@
     defaults: ["libc_defaults"],
     name: "libc",
     static_ndk_lib: true,
+    export_include_dirs: ["include"],
     product_variables: {
         platform_sdk_version: {
             asflags: ["-DPLATFORM_SDK_VERSION=%d"],