simulator: get CROSS_TOOL and EXEC_PATH from env

Simulator get it's way to Travis CI ready.

bsp/simulator/rtconfig.py

+import os
+
 # toolchains options
 ARCH='sim'
 #CROSS_TOOL='msvc' or 'gcc' or 'mingw'
@@ -5,6 +7,9 @@ ARCH='sim'
 # 'gcc' is for linux
 CROSS_TOOL='msvc'
 
+if os.getenv('RTT_CC'):
+	CROSS_TOOL = os.getenv('RTT_CC')
+
 # cross_tool provides the cross compiler
 # EXEC_PATH is the compiler execute path 
 if  CROSS_TOOL == 'gcc':
@@ -26,6 +31,9 @@ else :
     print "bad CROSS TOOL!"
     exit(1)
 
+if os.getenv('RTT_EXEC_PATH'):
+	EXEC_PATH = os.getenv('RTT_EXEC_PATH')
+
 BUILD = 'debug'
 #BUILD = ''