GPU Metal: pass the no-fast-math flags as separate arguments

GPUCA_METAL_NO_FAST_MATH_FLAGS is a string of two flags, appended to
METAL_FLAGS as one list element, so the Metal compiler got the single
argument '-fno-fast-math -ffp-contract=off' and rejected it: with
GPUCA_DETERMINISTIC_MODE set to NO_FAST_MATH or OPTO2 the Metal kernels
did not build. Split the string first.

Author: ktf

GPU/GPUTracking/Base/metal/CMakeLists.txt

@@ -28,7 +28,9 @@ set(METAL_BIN ${CMAKE_CURRENT_BINARY_DIR}/GPUReconstructionMetalCode)
 # relies on for GPUgeneric() and GPUdDefault().
 set(METAL_FLAGS -std=metal4.1 ${GPUCA_METAL_DENORMALS_FLAGS})
 if(GPUCA_DETERMINISTIC_MODE GREATER_EQUAL ${GPUCA_DETERMINISTIC_MODE_MAP_NO_FAST_MATH})
-  set(METAL_FLAGS ${METAL_FLAGS} ${GPUCA_METAL_NO_FAST_MATH_FLAGS})
+  # A string of several flags, which the custom commands below would pass as one
+  separate_arguments(GPUCA_METAL_NO_FAST_MATH_FLAGS_LIST UNIX_COMMAND "${GPUCA_METAL_NO_FAST_MATH_FLAGS}")
+  set(METAL_FLAGS ${METAL_FLAGS} ${GPUCA_METAL_NO_FAST_MATH_FLAGS_LIST})
 endif()
 set(METAL_DEFINES "-D$<JOIN:$<TARGET_PROPERTY:O2::GPUTracking,COMPILE_DEFINITIONS>,$<SEMICOLON>-D>"
             "-I$<JOIN:$<FILTER:$<TARGET_PROPERTY:O2::GPUTracking,INCLUDE_DIRECTORIES>,EXCLUDE,^/usr/include/?>,$<SEMICOLON>-I>"