This is Stanley Zhong's (a.k.a. qpwoeirut) repository for all things competitive programming.
Install g++ with HomeBrew.
My include directory is currently /usr/local/Cellar/gcc/10.2.0/include/c++/10.2.0.
You can find the include directory by doing g++-10 -v file.cpp and checking the directories listed after #include <...> search starts here.
On Macs, the backend of g++ is actually Clang, so you'll need to install the actual GCC for this.
Once you install it (probably through Homebrew), the command should be something like g++-x, where x is some number.
For example I'm using g++-10.
Inside the bits folder, run the command you normally use to compile files, but with an extra flag: -x c++-header.
Also don't include the -lm flag since apparently that breaks things. Not sure why but there's probably an explanation elsewhere on the internet.
This should generate a stdc++.h.gch file.
To use the precompiled file, just compile normally. Note that the compiler flags must be the same as the ones used to precompiled stdc++.h for this to work.