CMake: Fix Fortran cross-compilation support

[jschueller]

The current CMAKE_CROSSCOMPILING paths lead here to dummy commands "cmake -E env" being emitted that dont seem to do anything even when CROSSCOMPILING_PATH is set (#5720) as it must be followed by an actual command, and not another COMMAND entry:

cmake -E env: no command given

It seems CROSSCOMPILING_PATH is intented to pass environment variables to the emulator.
A cleaner way is to set them via a script that actually calls the emulator instead of adding CROSSCOMPILING_PATH to every executable target invocation.
Then this script would be passed as CMAKE_CROSSCOMPILING_EMULATOR instead of the emulator itself.
A common use-case is to pass WINEPATH to wine so that standard dlls are found when running mingw executables:

#!/bin/sh
mingw_prefix=/usr/i686-w64-mingw32
export WINEPATH=${mingw_prefix}/bin
/usr/bin/wine "$@"

Anyway we can simplify the two paths of the if/else, CMAKE_CROSSCOMPILING_EMULATOR being empty when CMAKE_CROSSCOMPILING is false.
Note that we need to use CMAKE_CROSSCOMPILING_EMULATOR explicitely here otherwise it would be omitted by cmake when generator expressions like these,
and you cannot always rely on binfmt_misc to forward to the right emulator.

/cc @byrnHDF

Tested with mingw from linux.

---

Important

Simplifies CMake cross-compilation by merging paths and using CMAKE_CROSSCOMPILING_EMULATOR consistently across multiple files.

• Behavior:
  • Simplifies cross-compilation by merging if/else paths in fortran/src/CMakeLists.txt, fortran/test/CMakeLists.txt, and hl/fortran/src/CMakeLists.txt.
  • Uses CMAKE_CROSSCOMPILING_EMULATOR consistently for executing target files.
• Commands:
  • Removes dummy command cmake -E env ${CROSSCOMPILING_PATH} in favor of CMAKE_CROSSCOMPILING_EMULATOR.
  • Ensures generated files must exist beforehand if CMAKE_CROSSCOMPILING_EMULATOR is not set.
• Testing:
  • Tested with MinGW from Linux.

^{This description was created by for f91fb3c. You can customize this summary. It will automatically update as commits are pushed.}

[brtnfld]

Location: config/toolchain/mingw64.cmake:28-29

Problem: The toolchain file sets CMAKE_CROSSCOMPILING_EMULATOR=wine64 without WINEPATH configuration. Current State:

set(CMAKE_CROSSCOMPILING_EMULATOR wine64) # Missing WINEPATH!
set(CROSSCOMPILING_PATH "WINEPATH=/usr/${TOOLCHAIN_PREFIX}/sys-root/mingw/bin/") # Ignored!

Option A: Simple solution:
set(CMAKE_CROSSCOMPILING_EMULATOR
env WINEPATH=/usr/${TOOLCHAIN_PREFIX}/sys-root/mingw/bin/ wine64
)

Option B (Wrapper script - cleaner):

Create wrapper script at configure time

file(WRITE "${CMAKE_BINARY_DIR}/mingw-wine-wrapper.sh" "#!/bin/sh
export WINEPATH=/usr/${TOOLCHAIN_PREFIX}/sys-root/mingw/bin
exec wine64 "$@"
")
file(CHMOD "${CMAKE_BINARY_DIR}/mingw-wine-wrapper.sh"
PERMISSIONS OWNER_READ OWNER_WRITE OWNER_EXECUTE)

set(CMAKE_CROSSCOMPILING_EMULATOR "${CMAKE_BINARY_DIR}/mingw-wine-wrapper.sh")

ALSO:

Current:

if (NOT CMAKE_CROSSCOMPILING OR (CMAKE_CROSSCOMPILING AND CMAKE_CROSSCOMPILING_EMULATOR))

Simplified:

if (NOT CMAKE_CROSSCOMPILING OR CMAKE_CROSSCOMPILING_EMULATOR)

Summary:

Proposed Change to config/toolchain/mingw64.cmake:

Untested

# CMAKE_CROSSCOMPILING_EMULATOR: Wrapper script for running Windows binaries during build
# Must include WINEPATH so Wine can find system DLLs
file(WRITE "${CMAKE_BINARY_DIR}/cmake-wine-wrapper.sh" "#!/bin/sh
# Wine wrapper for MinGW cross-compilation
export WINEPATH=/usr/${TOOLCHAIN_PREFIX}/sys-root/mingw/bin
exec wine64 \"$@\"
")
file(CHMOD "${CMAKE_BINARY_DIR}/cmake-wine-wrapper.sh" 
     PERMISSIONS OWNER_READ OWNER_WRITE OWNER_EXECUTE GROUP_READ GROUP_EXECUTE)

set(CMAKE_CROSSCOMPILING_EMULATOR "${CMAKE_BINARY_DIR}/cmake-wine-wrapper.sh")

# CROSSCOMPILING_PATH: Used by CTest ENVIRONMENT property for test execution
# This is separate from CMAKE_CROSSCOMPILING_EMULATOR and still needed for tests
set(CROSSCOMPILING_PATH "WINEPATH=/usr/${TOOLCHAIN_PREFIX}/sys-root/mingw/bin/")

[jschueller]

@brtnfld no need for cmake to generate the wrapper script, it can be a preexisting file like the toolchain script, see the file wine64.sh I added