Let the build script use a default for toolchain

The `cmake` directory already contains several toolchain files for
various platforms (operating system + architecture). However,
`tools/build.py` does not define a toolchain file for cmake unless
explicitly specified. This patch changes the script to look into
the `cmake` directory for a file named
`toolchain_$(os)_$(arch).cmake` and, if found, pass that to cmake
by default.

OS and arch are determined by `os.uname()`. As Linux on Raspberry
Pi identifies itself as "armv7l", the legacy "armv7l-hf" arch name
is shortened to "armv7l". This way, building jerry on RPi
(natively, not cross) becomes possible by simply running
`tools/build.py` without any extra options.

JerryScript-DCO-1.0-Signed-off-by: Akos Kiss akiss@inf.u-szeged.hu

cmake/toolchain_linux_armv7l.cmake

@@ -13,7 +13,7 @@
 # limitations under the License.
 
 set(CMAKE_SYSTEM_NAME Linux)
-set(CMAKE_SYSTEM_PROCESSOR armv7l-hf)
+set(CMAKE_SYSTEM_PROCESSOR armv7l)
 
 set(CMAKE_C_COMPILER arm-linux-gnueabihf-gcc)
 #

cmake/toolchain_mcu_stm32f3.cmake

@@ -15,7 +15,7 @@
 include(CMakeForceCompiler)
 
 set(CMAKE_SYSTEM_NAME MCU)
-set(CMAKE_SYSTEM_PROCESSOR armv7l-hf)
+set(CMAKE_SYSTEM_PROCESSOR armv7l)
 set(CMAKE_SYSTEM_VERSION STM32F3)
 
 set(FLAGS_COMMON_ARCH -mlittle-endian -mthumb -mcpu=cortex-m4 -march=armv7e-m -mfpu=fpv4-sp-d16 -mfloat-abi=hard)

cmake/toolchain_mcu_stm32f4.cmake

@@ -15,7 +15,7 @@
 include(CMakeForceCompiler)
 
 set(CMAKE_SYSTEM_NAME MCU)
-set(CMAKE_SYSTEM_PROCESSOR armv7l-hf)
+set(CMAKE_SYSTEM_PROCESSOR armv7l)
 set(CMAKE_SYSTEM_VERSION STM32F4)
 
 set(FLAGS_COMMON_ARCH -mlittle-endian -mthumb -mcpu=cortex-m4 -march=armv7e-m -mfpu=fpv4-sp-d16 -mfloat-abi=hard)