Simplify the error output on failed Command invocation

[madsmtm]

Passing around the program we wanted to execute in command_helpers.rs is unnecessary, we can retrieve it from Command::get_program instead when required, and that path is usually more descriptive anyhow.

Motivation

I'm currently debugging this. The error that cc-rs gives is:

error occurred: Command "sccache" "aarch64-unknown-fuchsia-clang" "-O3" "-ffunction-sections" "-fdata-sections" "-fPIC" "-g" "-fno-omit-frame-pointer" "--target=aarch64-unknown-fuchsia" "-I" "/checkout/src/llvm-project/compiler-rt/lib/builtins" "-fno-builtin" "-fvisibility=hidden" "-ffreestanding" "-fomit-frame-pointer" "-ffile-prefix-map=/checkout/src/llvm-project/compiler-rt=." "-DCOMPILER_RT_HAS_FLOAT16" "-DVISIBILITY_HIDDEN" "-o" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2-std/aarch64-unknown-fuchsia/release/build/compiler_builtins-6830d4e928982f93/out/670c1ed24249df13-aarch64.o" "-c" "/checkout/src/llvm-project/compiler-rt/lib/builtins/cpu_model/aarch64.c" with args aarch64-unknown-fuchsia-clang did not execute successfully (status code exit status: 1).

This was confusing, as "aarch64-unknown-fuchsia-clang" is really the compiler and not "args". Besides, I didn't actually need to know that the tool we "wanted" to invoke; that is evident from the pretty-printed command line arguments.

With this PR, the above error would have been:

error occurred: command did not execute successfully (status code 1): "sccache" "aarch64-unknown-fuchsia-clang" "-O3" "-ffunction-sections" "-fdata-sections" "-fPIC" "-g" "-fno-omit-frame-pointer" "--target=aarch64-unknown-fuchsia" "-I" "/checkout/src/llvm-project/compiler-rt/lib/builtins" "-fno-builtin" "-fvisibility=hidden" "-ffreestanding" "-fomit-frame-pointer" "-ffile-prefix-map=/checkout/src/llvm-project/compiler-rt=." "-DCOMPILER_RT_HAS_FLOAT16" "-DVISIBILITY_HIDDEN" "-o" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2-std/aarch64-unknown-fuchsia/release/build/compiler_builtins-6830d4e928982f93/out/670c1ed24249df13-aarch64.o" "-c" "/checkout/src/llvm-project/compiler-rt/lib/builtins/cpu_model/aarch64.c"

Which is shorter, and makes it clearer where the command starts and ends (after the colon and at the end of the line).

[NobodyXu]

Thanks, just one minor nit for error message