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/Editor/Util/ImageUtil.cpp

@@ -143,7 +143,8 @@ bool CImageUtil::LoadPGM(const QString& fileName, CImageEx& image)
     fseek(file, 0, SEEK_SET);
 
     char* str = new char[fileSize];
-    fread(str, fileSize, 1, file);
+
+    [[maybe_unused]] auto bytesRead = fread(str, fileSize, 1, file);
 
     [[maybe_unused]] char* nextToken = nullptr;
     token = azstrtok(str, 0, seps, &nextToken);