[BSP] TM4C129X: Move the IAR compile argument to IAR condition branch.

bsp/tm4c129x/libraries/SConscript

@@ -6,6 +6,7 @@ from building import *
 cwd     = GetCurrentDir()
 src = Glob('driverlib/*.c')
 SrcRemove(src, 'onewire.c')
+CCFLAGS = ''
 
 # add for startup script 
 if rtconfig.CROSS_TOOL == 'gcc':
@@ -14,9 +15,10 @@ elif rtconfig.CROSS_TOOL == 'keil':
     src += ['startup/startup_rvmdk.S']
 elif rtconfig.CROSS_TOOL == 'iar':
     src += ['startup/startup_ewarm.c']
+    CCFLAGS += ' --diag_suppress=pe177'
 
 CPPPATH = [cwd, cwd + '/inc', cwd + '/driverlib']
-CCFLAGS = ' --diag_suppress=pe177'
+
 
 CPPDEFINES = [rtconfig.PART_TYPE]
 group = DefineGroup('Libraries', src, depend = [''], CPPPATH = CPPPATH, CPPDEFINES = CPPDEFINES, CCFLAGS = CCFLAGS)