NMSIS: remove some gcc diagnostic options

Fixed issue #32 in github

Signed-off-by: Huaqi Fang <578567190@qq.com>

NMSIS/Core/Include/nmsis_gcc.h

@@ -42,11 +42,6 @@
  * The header file <b>nmsis_compiler.h</b> is also included by each Device Header File <device.h> so that these definitions are available.
  *   @{
  */
-/* ignore some GCC warnings */
-#pragma GCC diagnostic push
-#pragma GCC diagnostic ignored "-Wsign-conversion"
-#pragma GCC diagnostic ignored "-Wconversion"
-#pragma GCC diagnostic ignored "-Wunused-parameter"
 
 /* Fallback for __has_builtin */
 #ifndef __has_builtin