Enhanced stack-traces via backwards library

Backwards library provides basic stack-traces of a crash and enhanced
stack-traces by using libdw and/or libbfd.
This patch will detect if either library exists on the system and set
the appropriate compiler directives accordingly.
The libraries will be packages as part of the Lambda zip file.

CMakeLists.txt

@@ -1,31 +1,19 @@
 cmake_minimum_required(VERSION 3.5)
 set(CMAKE_CXX_STANDARD 11)
 project(aws-lambda-runtime
-    VERSION 0.1.0
+    VERSION 0.2.0
     LANGUAGES CXX)
 
 option(ENABLE_TESTS "Enables building the test project, requires AWS C++ SDK." OFF)
 
-include(CheckCXXSourceCompiles)
 include(CheckCXXCompilerFlag)
 
-check_cxx_source_compiles("
-#include <execinfo.h>
-
-int main() {
-void *buffer[5];
-int nptrs = backtrace(buffer, 5);
-char **strings = backtrace_symbols(buffer, nptrs);
-
-return !!strings;
-}"  HAVE_BACKTRACE)
-
-
 check_cxx_compiler_flag("-Wl,-flto" LTO_CAPABLE)
 
 add_library(${PROJECT_NAME}
     "src/logging.cpp"
     "src/runtime.cpp"
+    "src/backward.cpp"
     "${CMAKE_CURRENT_BINARY_DIR}/version.cpp"
     )
 
@@ -39,10 +27,6 @@ find_package(CURL REQUIRED)
 target_link_libraries(${PROJECT_NAME} PRIVATE ${CURL_LIBRARIES})
 target_include_directories(${PROJECT_NAME} PRIVATE ${CURL_INCLUDE_DIRS})
 
-if(HAVE_BACKTRACE)
-    target_compile_definitions(${PROJECT_NAME} PRIVATE -DHAVE_BACKTRACE)
-endif()
-
 target_compile_options(${PROJECT_NAME} PRIVATE
     "-fno-exceptions"
     "-fno-rtti"
@@ -53,6 +37,20 @@ target_compile_options(${PROJECT_NAME} PRIVATE
     "-Wconversion"
     "-Wno-sign-conversion")
 
+find_library(DW_LIB NAMES dw)
+if (NOT DW_LIB STREQUAL DW_LIB-NOTFOUND)
+    message("-- Enhanced stack-traces are enabled via libdw: ${DW_LIB}")
+    target_compile_definitions(${PROJECT_NAME} PRIVATE "BACKWARD_HAS_DW=1")
+    target_link_libraries(${PROJECT_NAME} PUBLIC "${DW_LIB}")
+else()
+    find_library(BFD_LIB NAMES bfd)
+    if (NOT BFD_LIB STREQUAL BFD_LIB-NOTFOUND)
+        message("-- Enhanced stack-traces are enabled via libbfd: ${BFD_LIB}")
+        target_compile_definitions(${PROJECT_NAME} PRIVATE "BACKWARD_HAS_BFD=1")
+        target_link_libraries(${PROJECT_NAME} PRIVATE "${BFD_LIB}")
+    endif()
+endif()
+
 if (LOG_VERBOSITY)
     target_compile_definitions(${PROJECT_NAME} PRIVATE "AWS_LAMBDA_LOG=${LOG_VERBOSITY}")
 elseif(CMAKE_BUILD_TYPE STREQUAL Debug)