cmake - add warning flags for clang, gcc etc.

cmake/OpusConfig.cmake

@@ -78,3 +78,15 @@ else()
   check_flag(STACK_PROTECTOR -fstack-protector-strong)
   check_flag(HIDDEN_VISIBILITY -fvisibility=hidden)
 endif()
+
+if(NOT MSVC)
+  set(WARNING_LIST -Wall -W -Wstrict-prototypes -Wextra -Wcast-align -Wnested-externs -Wshadow)
+  include(CheckCCompilerFlag)
+  foreach(WARNING_FLAG ${WARNING_LIST})
+    string(REPLACE - "" WARNING_VAR ${WARNING_FLAG})
+    check_c_compiler_flag(${WARNING_FLAG} ${WARNING_VAR}_SUPPORTED)
+    if(${WARNING_VAR}_SUPPORTED)
+      add_compile_options(${WARNING_FLAG})
+    endif()
+  endforeach()
+endif()
\ No newline at end of file