cmake: Use custom target to compile timeit/fpcmp

[MatzeB]

Summary

When cross compiling the testsuite we still need to compile timeit/fpcmp
for the host machine. These two files are extremely simple C files so adding a custom
command that just runs "cc timeit.c -o timeit" should do the trick.

[beanz]

Since these are really simple source files, it is probably better to check CMAKE_CROSSCOMPILING and when cross-compiling use ExternalProject to configure host versions of the tools.

[MatzeB]

In D15004#298651, @beanz wrote:

Since these are really simple source files, it is probably better to check CMAKE_CROSSCOMPILING and when cross-compiling use ExternalProject to configure host versions of the tools.

Looks like my cmake-foo is not strong enough for ExternalProject_Add.

For one CMAKE_CROSSCOMPILING is not set for me even though I am happily crosscompiling to aarch64 by just passing the respective -arch arm64 CFLAGS. Apart from that AddExternalProject_Add has a LOT of options and I am not really sure which ones I need or what to set them to. Are you sure this is better/simpler than two simple custom commands?

[beanz]

CMAKE_CROSSCOMPILING is set by CMake when you explicitly set CMAKE_SYSTEM_NAME. Instead of setting the -arch flag, try setting CMAKE_TOOLCHAIN_FILE to point to the ios.cmake file in LLVM trunk, and set CMAKE_OSX_ARCHITECTURES to arm64.

There is an example of cross compiling LLVM here: http://llvm.org/docs/GettingStarted.html#cross-compiling-llvm

[jmolloy]

Resigning from this as it's stalled.

[MatzeB]

Abandoning this for now as the current solution seems to work good enough.

tools/CMakeLists.txt

 add_executable(timeit-target timeit.c)
 
-# FIXME: These need to be host-compiled, if we're cross compiling.
 # FIXME: Replicate Makefile.tools's logic for determining whether to use fpcmp/fpcmp.sh
-add_executable(fpcmp fpcmp.c)
-add_executable(timeit timeit.c)
+set(TEST_SUITE_HOST_CC "cc" CACHE STRING "C compiler targetting the host")
+mark_as_advanced(TEST_SUITE_HOST_CC)
+add_custom_target(fpcmp
+  COMMAND ${TEST_SUITE_HOST_CC} ${CMAKE_CURRENT_SOURCE_DIR}/fpcmp.c -o ${CMAKE_CURRENT_BINARY_DIR}/fpcmp
+  DEPENDS ${CMAKE_CURRENT_SOURCE_DIR}/fpcmp.c
+)
+add_custom_target(timeit
+  COMMAND ${TEST_SUITE_HOST_CC} ${CMAKE_CURRENT_SOURCE_DIR}/timeit.c -o ${CMAKE_CURRENT_BINARY_DIR}/timeit
+  DEPENDS ${CMAKE_CURRENT_SOURCE_DIR}/timeit.c
+)