Moved include/backtrace to libbacktrace/include

Export libbacktrace_headers

Bug: 33241851
Test: Build sailfish
Change-Id: Iba310ffc21d17ba542bed954a960ab305037061c
diff --git a/libbacktrace/Android.bp b/libbacktrace/Android.bp
index 8f74a1a..7de72a8 100644
--- a/libbacktrace/Android.bp
+++ b/libbacktrace/Android.bp
@@ -55,6 +55,11 @@
     "UnwindPtrace.cpp",
 ]
 
+cc_library_headers {
+    name: "libbacktrace_headers",
+    export_include_dirs: ["include"],
+}
+
 cc_library {
     name: "libbacktrace",
     defaults: ["libbacktrace_common"],
@@ -64,6 +69,8 @@
         "BacktraceMap.cpp",
     ],
 
+    export_include_dirs: ["include"],
+
     target: {
         darwin: {
             enabled: true,