Moved include/backtrace to libbacktrace/include

Export libbacktrace_headers

cherry-pick from commit 8f2c28d572

Bug: 33241851
Test: Build sailfish
Change-Id: Ied4168425ded95724d051ffdc9965c5927bc05ae
Merged-In: Iba310ffc21d17ba542bed954a960ab305037061c

include/backtrace

@@ -0,0 +1 @@
+../libbacktrace/include/backtrace

libbacktrace/Android.bp

@@ -55,6 +55,11 @@ libbacktrace_sources = [
     "UnwindPtrace.cpp",
 ]
 
+cc_library_headers {
+    name: "libbacktrace_headers",
+    export_include_dirs: ["include"],
+}
+
 cc_library {
     name: "libbacktrace",
     defaults: ["libbacktrace_common"],
@@ -64,6 +69,8 @@ cc_library {
         "BacktraceMap.cpp",
     ],
 
+    export_include_dirs: ["include"],
+
     target: {
         darwin: {
             enabled: true,