modify gcc/Makefile.posix

nRF5_SDK_15.3.0/components/toolchain/gcc/Makefile.posix

@@ -1,3 +1,3 @@
-GNU_INSTALL_ROOT = /usr/local/gcc-arm-none-eabi-8-2019-q3-update/bin/
-GNU_VERSION = 8.3.1
+GNU_INSTALL_ROOT = /usr/bin/
+GNU_VERSION = 10.3.1
 GNU_PREFIX = arm-none-eabi