Import backtrace-cpp and integrate it into our main executable

Upstream release
https://github.com/bombela/backward-cpp/archive/v1.3.tar.gz

external/backtrace-cpp/test_package/conanfile.py

@@ -0,0 +1,15 @@
+from conans import ConanFile, CMake
+import os
+
+class TestBackward(ConanFile):
+    settings = 'os', 'compiler', 'build_type', 'arch'
+    requires = 'cmake-utils/0.0.0@Manu343726/testing', 'backward/0.0.0@Manu343726/testing'
+    generators = 'cmake'
+
+    def build(self):
+        cmake = CMake(self.settings)
+        self.run('cmake {} {}'.format(self.conanfile_directory, cmake.command_line))
+        self.run('cmake --build . {}'.format(cmake.build_config))
+
+    def test(self):
+        self.run(os.path.join('.', 'bin', 'example'))