[flang]enable execute_command_line tests

[yiwu0b11]

build and pass all three tests on Linux, will test it on Windows later today

[tblah]

LGTM: execute command line was added in llvm/llvm-project#74077

[yiwu0b11]

It will compile and run on Windows, but it does not behave the same. This is because Windows has different command, dir <=> ls, timeout <=> sleep.

[tarunprabhu]

Tested on Linux on x86 and it looks to be fine. Thanks for enabling these.

[tarunprabhu]

It will compile and run on Windows, but it does not behave the same. This is because Windows has different command, dir <=> ls, timeout <=> sleep.

Just out of curiosity. What do you mean by this?

[yiwu0b11]

It will compile and run on Windows, but it does not behave the same. This is because Windows has different command, dir <=> ls, timeout <=> sleep.

Just out of curiosity. What do you mean by this?

This is because execute_command_line calls std::system, and on Windows that is cmd. cmd doesn't have ls, the Windows equivalent command is dir, and for timeout for sleep. It will compile and run correct based on the standard, however, the printout from the execution won't be the same on Linux.
For example:

llvm-test-suite/Fortran/gfortran/regression/execute_command_line_1.f90

Line 10 in 394a62e

call execute_command_line ("ls *.f90")

This will compile but will cause:

fatal Fortran runtime error(.......regression\execute_command_line_1.f90:31): Invalid command quit with exit status code: 1

as this is expected based on the standard, if cmdstat is assigned with non-zero value but the CMDSTAT variable is not present, error termination is initiated.
https://github.com/llvm/llvm-project/blob/c9a6e993f7b349405b6c8f9244cd9cf0f56a6a81/flang/docs/Intrinsics.md?plain=1#L905