Custom built GCC search paths

[firasuke]

Hey there, I'd like to thank you for your time and for your work on the mold linker.

I am working on an independent Linux distribution, where I have a custom built toolchain that utilizes gcc and musl.

I was trying to configure the toolchain to use mold as its linker, and I was successful. However, I faced some issues.

Here are my notes on how I fixed those issues:

• Custom built GCCs have custom search directories. Even though I have version 12.2.0, adding -fuse-ld=mold was not sufficient for my custom gcc to find the host's mold (provided by distribution's package manager) or my custom mold (as I was getting the following error collect2: fatal error: cannot find 'ld' mold, which is why I had to add -B/path/to/directory/where/custom/mold/is to my CFLAGS along with -fuse-ld=mold to get it working.
• Most packages linked just fine, until I stumbled upon packages which used autoreconf and libtool to create .la files. Apparently libtool likes to strip flags when linking. This was troublesome because I am passing -B/path/to/directory/where/custom/mold/is in my CFLAGS and it was being removed, so my custom gcc could no longer find mold, giving the same error as above.
• You can workaround this by modifying GCC_EXEC_PREFIX which is not desirable for many reasons.
• The solution I found was to provide a symbolic link to mold in the search directories of the custom built gcc (which can be listed by running gcc -print-search-dirs).
• The symbolic link was installed in /custom/toolchain/tuple/bin where binutils already keeps its hardlinks to ../../bin including ld.bfd, which is why I issued the command ln -fs ../../bin/mold /custom/toolchain/tuple/bin/ld.mold.

I understand that this is not an upstream issue, but I thought it would help those who encounter a similar issue in the future.

One suggestion I have is to add a note to the documentation (the section where it talks about installing / running / using mold) reminding users who are working with custom toolchains to include mold in their compiler's custom search directory.

Keep up the great work!