Fix test program for old compilers.

test/extension-tests/successful-build/project-folder/cmakelists.txt

@@ -2,6 +2,7 @@ cmake_minimum_required(VERSION 3.0.0)
 project(TestBuildProcess VERSION 0.1.0)
 
 add_executable(TestBuildProcess main.cpp)
+set_property(TARGET TestBuildProcess PROPERTY CXX_STANDARD 98)
 
 add_custom_command(
     TARGET TestBuildProcess

test/extension-tests/successful-build/project-folder/main.cpp

@@ -21,8 +21,8 @@ std::string getCompilerName() {
 }
 
 std::string get_env_var(const std::string& key) {
-    const auto env = std::getenv(key.c_str());
-    return env != nullptr ? env : "";
+    const char* env = std::getenv(key.c_str());
+    return env != NULL ? env : "";
 }
 
 int main(int, char**) {