https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108534
--- Comment #2 from Ian Lance Taylor <ian at airs dot com> ---
Yes, it's a relative path, such as
#line 1 "cgo-gcc-prolog"
These are dummy but informative line markers used to separate generated code
from user-written code, so that compiler error messages report problems in the
right place.
The compiler is being executed in a temporary directory created during the
build, so the working directory is meaningless. Other references to files in
that temporary directory are rewritten by a -fdebug-prefix-map option.
Unfortunately, that option fails to rename the working directory that is pulled
in for the relative #line option.
