cmake: add ZIG_BUILD_ARGS_OVERRIDE string option

[BratishkaErik]

Useful when someone wants to pass argument that is not yet exposed to CMake via "ZIG_WHATEVER" option, for example "--search-prefix" from here: #18434 .

Also change order of arguments in cmake/install.cmake to be the same as in CMakeLists.txt, so that "--prefix" can be overriden in both steps.

Also bump minimum CMake version to "3.9".

[BratishkaErik]

Forgot to bump CMake version in README, fixed now.

[andrewrk]

why do you need to override arbitrary arguments? it does not specify intent clearly enough.

[BratishkaErik]

why do you need to override arbitrary arguments? it does not specify intent clearly enough.

For example, to pass "-Ddebug_extensions" to zig2 when building stage3. This way, we don't need to spend extra time building stage4, since all args are used together in one step (stage3).

Or if someone can't even build stage3, like in mentioned issue.

UPD: and there is no way to tell CMake from command line "build targets up to/excluding stage3" (AFAIK), and bootstrap.c builds stages with have_llvm = false, so users can't just build zig2 alone with CMake and then pass needed args to it.

[erikarvstedt]

You can build just stage 2 with make zig2 (when using the makefile generator).

Maybe this simpler approach, which adds var ZIG_EXTRA_BUILD_ARGS to amend the existing var setup, is a better fit for just adding some args to the stage3 build.

[BratishkaErik]

You can build just stage 2 with make zig2 (when using the makefile generator).

Maybe this simpler approach, which adds var ZIG_EXTRA_BUILD_ARGS to amend the existing var setup, is a better fit for just adding some args to the stage3 build.

Thank you for info, this may sound silly, but I completely forgot about this. I changed this PR complwtely, now this is a general cleanup of CMakeLists.txt and revival of #12747 .

[BratishkaErik]

You can build just stage 2 with make zig2 (when using the makefile generator).
Maybe this simpler approach, which adds var ZIG_EXTRA_BUILD_ARGS to amend the existing var setup, is a better fit for just adding some args to the stage3 build.

Thank you for info, this may sound silly, but I completely forgot about this. I changed this PR complwtely, now this is a general cleanup of CMakeLists.txt and revival of #12747 .

Oops, I closed it by removing branch and can't reopen it, new PR here #19969 .