Require HEXAGON_ARM_SYSROOT for arm-linux-gnueabihf

The Toolchain-arm-linux-gnueabihf.cmake is currently used for
the SnapdragonFlight Apps processor.

The sysroot is required for cross building for Ubuntu 14.04 armhf.

Signed-off-by: Mark Charlebois <charlebm@gmail.com>

cmake/toolchains/Toolchain-arm-linux-gnueabihf.cmake

@@ -23,6 +23,12 @@ else()
         set(HEXAGON_TOOLS_ROOT $ENV{HEXAGON_SDK_ROOT})
 endif()
 
+if ("$ENV{HEXAGON_ARM_SYSROOT}" STREQUAL "")
+        message(FATAL_ERROR "HEXAGON_ARM_SYSROOT not set")
+else()
+        set(HEXAGON_TOOLS_ROOT $ENV{HEXAGON_ARM_SYSROOT})
+endif()
+
 # this one is important
 set(CMAKE_SYSTEM_NAME Generic)
 
@@ -69,7 +75,7 @@ foreach(tool echo patch grep rm mkdir nm genromfs cp touch make unzip)
 	endif()
 endforeach()
 
-set(C_FLAGS "--sysroot=${HEXAGON_SDK_ROOT}/sysroot")
+set(C_FLAGS "--sysroot=${HEXAGON_ARM_SYSROOT}")
 set(LINKER_FLAGS "-Wl,-gc-sections")
 set(CMAKE_EXE_LINKER_FLAGS ${LINKER_FLAGS})
 set(CMAKE_C_FLAGS ${C_FLAGS})