[cmake] Honor CMAKE_VERBOSE_MAKEFILE when building external projects

[DimitryAndric]

When the top-level CMake invocation has CMAKE_VERBOSE_MAKEFILE=ON, indicating the user wants to have verbose builds (i.e. all executed commands explicitly echoed), some of the subprojects and runtimes (such as compiler-rt, libcxx, etc) do not build in verbose mode. For example, with Ninja:

[ 99% 6252/6308] cd /build/runtimes/builtins-bins && /usr/local/bin/cmake --build .
[  0% 6/308] Building C object CMakeFiles/clang_rt.builtins-i386.dir/absvti2.c.o
[  0% 7/308] Building C object CMakeFiles/clang_rt.builtins-i386.dir/absvdi2.c.o
[  0% 8/308] Building C object CMakeFiles/clang_rt.builtins-i386.dir/absvsi2.c.o
...

This is because llvm_ExternalProject_Add() and add_custom_libcxx() use CMake's ExternalProject_Add() function to configure such subproject builds, and do not pass through the CMAKE_VERBOSE_MAKEFILE setting.

Similar to what is done in clang/CMakeLists.txt, add -DCMAKE_VERBOSE_MAKEFILE=ON to the ExternalProject_Add() invocations in llvm_ExternalProject_Add() and add_custom_libcxx(), whenever the top-level CMake invocation had CMAKE_VERBOSE_MAKEFILE turned on.

[MaskRay]

I have checked that CMAKE_VERBOSE_MAKEFILE does not affect Ninja, so perhaps most people will not observe anything.

[DimitryAndric]

I got this suggestion from https://discourse.cmake.org/t/no-verbose-output-when-building-an-external-project-with-ninja/1113, where they recommend using CMAKE_VERBOSE_BUILD with Ninja. For GNU make it is not necessary since you can pass VERBOSE=1 as a variable on the command line, and it will automatically be passed down to all sub-makes.

As an example, when I do a top-level configure with CMake -G Ninja -D CMAKE_VERBOSE_BUILD:BOOL=ON with this patch, I now get (for the builtins lib, for example):

-- Build files have been written to: /build/runtimes/builtins-bins
[ 30% 4/10] cd /build/runtimes/builtins-bins && /usr/local/bin/cmake --build .
Change Dir: '/build/runtimes/builtins-bins'

Run Build Command(s): /usr/local/bin/ninja -v
[  3% 6/29] /build/./bin/clang --target=x86_64-unknown-freebsd15.0 -DVISIBILITY_HIDDEN  -O3 -DNDEBUG -m32 -fno-lto -std=c11 -fPIC -fno-builtin -fvisibility=hidden -fomit-frame-pointer -MD -MT CMakeFiles/clang_rt.builtins-i386.dir/mulosi4.c.o -MF CMakeFiles/clang_rt.builtins-i386.dir/mulosi4.c.o.d -o CMakeFiles/clang_rt.builtins-i386.dir/mulosi4.c.o -c /share/dim/src/llvm/llvm-project/compiler-rt/lib/builtins/mulosi4.c
[  6% 7/29] /build/./bin/clang --target=x86_64-unknown-freebsd15.0 -DVISIBILITY_HIDDEN  -O3 -DNDEBUG -m32 -fno-lto -std=c11 -fPIC -fno-builtin -fvisibility=hidden -fomit-frame-pointer -MD -MT CMakeFiles/clang_rt.builtins-i386.dir/muldc3.c.o -MF CMakeFiles/clang_rt.builtins-i386.dir/muldc3.c.o.d -o CMakeFiles/clang_rt.builtins-i386.dir/muldc3.c.o -c /share/dim/src/llvm/llvm-project/compiler-rt/lib/builtins/muldc3.c
...