update rtconfig.py to remove -nostdinc

bsp/qemu-virt-rv64/rtconfig.py

@@ -5,10 +5,7 @@ ARCH        ='risc-v'
 CPU         ='virt64'
 CROSS_TOOL  ='gcc'
 
-if os.getenv('RTT_ROOT'):
-    RTT_ROOT = os.getenv('RTT_ROOT')
-else:
-    RTT_ROOT = os.path.join(os.getcwd(), '..', '..')
+RTT_ROOT = os.getenv('RTT_ROOT') or os.path.join(os.getcwd(), '..', '..')
 
 if os.getenv('RTT_CC'):
     CROSS_TOOL = os.getenv('RTT_CC')
@@ -27,7 +24,7 @@ BUILD = 'debug'
 
 if PLATFORM == 'gcc':
     # toolchains
-    PREFIX  = 'riscv64-unknown-elf-'
+    PREFIX  = os.getenv('RTT_CC_PREFIX') or 'riscv64-unknown-elf-'
     CC      = PREFIX + 'gcc'
     CXX     = PREFIX + 'g++'
     AS      = PREFIX + 'gcc'
@@ -38,10 +35,10 @@ if PLATFORM == 'gcc':
     OBJDUMP = PREFIX + 'objdump'
     OBJCPY  = PREFIX + 'objcopy'
 
-    DEVICE  = ' -mcmodel=medany -march=rv64imafdc -mabi=lp64'
-    CFLAGS  = DEVICE + ' -fvar-tracking -ffreestanding -fno-common -ffunction-sections -fdata-sections -fstrict-volatile-bitfields -nostdinc '
+    DEVICE  = ' -mcmodel=medany -march=rv64imafdc -mabi=lp64d'
+    CFLAGS  = DEVICE + ' -fvar-tracking -ffreestanding -fno-common -ffunction-sections -fdata-sections -fstrict-volatile-bitfields'
     AFLAGS  = ' -c' + DEVICE + ' -x assembler-with-cpp'
-    LFLAGS  = DEVICE + ' -nostartfiles -Wl,--gc-sections,-Map=rtthread.map,-cref,-u,_start -T link.lds -lc -lm '
+    LFLAGS  = DEVICE + ' -nostartfiles -Wl,--gc-sections,-Map=rtthread.map,-cref,-u,_start -T link.lds'
     CPATH   = ''
     LPATH   = ''