[sconscript.platform] 优化针对编译器判断的脚本

- 删除啰嗦的代码
related: https://github.com/RT-Thread/rt-thread/issues/3046

components/drivers/spi/SConscript

@@ -25,13 +25,12 @@ if GetDepend('RT_USING_SFUD'):
     CPPPATH += [cwd + '/sfud/inc']
     if GetDepend('RT_SFUD_USING_SFDP'):
         src_device += ['sfud/src/sfud_sfdp.c']
-    if rtconfig.CROSS_TOOL == 'gcc':
+    if rtconfig.PLATFORM == 'gcc':
+        LOCAL_CCFLAGS += ' -std=c99'
+    elif rtconfig.PLATFORM == 'armcc':
+        LOCAL_CCFLAGS += ' --c99'
+    elif rtconfig.PLATFORM == 'armclang':
         LOCAL_CCFLAGS += ' -std=c99'
-    elif rtconfig.CROSS_TOOL == 'keil':
-        if rtconfig.PLATFORM == 'armcc':
-            LOCAL_CCFLAGS += ' --c99'
-        elif rtconfig.PLATFORM == 'armclang':
-            LOCAL_CCFLAGS += ' -std=c99'
 
 src += src_device