When rebuilding in an already built directory, cmake does use
the cache file, containing what variables were set to previously.
When changing build configuration (building with a different prefix,
or changing build configurations) this can often result in failed
cmake runs.
Wipe the cache (and the rest of the cmake temp files) by default.
This makes sure that the full cmake configuration is run each time
when running the build scripts, just like it does the first time.
(This doesn't remove the build artifacts; if nothing of significance
has changed, ninja would still reuse old built files.)
By setting the env variable NO_RECONF, this behaviour can be skipped,
rerunning cmake without wiping the cache inbetween. (For cases where
the user knows that the configuration hasn't changed since the last
build, this can speed up the cmake execution time a bit.)
This command isn't a standard tool; different distributions have
different implementations, and e.g. Fedora doesn't ship it by
default.
Settle on using "command -v $tool >/dev/null" for tests about whether
a tool is available. (We could also use "hash $tool 2>/dev/null" as we
already had in build-all.sh, but settling on using "command -v"
everywhere, for consistency and simplicity.)
This includes building universal binaries (for arm64 and x86_64)
and targeting an older minimum deployment target.
(Before 1919720fdd348ca568b235bf3f1357c198eccd15 in llvm-project,
Jan 2022, building lldb's debugserver failed, if building for macOS
for multiple architectures, or for an architecture other than the
current host.)
Building this tool requires having a full LLVM build available;
either by installing without LLVM_INSTALL_TOOLCHAIN_ONLY (and not
stripping the llvm installation yet) or by pointing it at the
LLVM build directory instead. The latter works better for our
normal build flows.
Martin Storsjö