Clang/GCC compiler settings update [SECURITY] (#7358)

- Add the following compilation flags for clang
  -fpie
  -fstack-protector-all
  -fstack-check (non-release)

- Add the following compilation flags for gcc
  -fpie
  -fstack-protector-all

- Fix -Wunused-result errors from above compilation flag updates

- Add _FORTIFY_SOURCE=2 to GCC DEFINES

Signed-off-by: Steve Pham <82231385+spham-amzn@users.noreply.github.com>

Code/Tools/AzTestRunner/Platform/Common/platform_host_posix.cpp

@@ -13,7 +13,7 @@ namespace AzTestRunner
 {
     void set_quiet_mode()
     {
-        freopen("/dev/null", "a", stdout);
+        [[maybe_unused]] auto freopenResult = freopen("/dev/null", "a", stdout);
     }
 
     const char* get_current_working_directory()
@@ -24,7 +24,7 @@ namespace AzTestRunner
 
     void pause_on_completion()
     {
-        system("pause");
+        [[maybe_unused]] auto systemResult = system("pause");
     }
 
 }