[bug#52499] [PATCH] gnu: Fix build error of libpfm4.

[Leo Famulari <leo@famulari.name>]

On Tue, Dec 14, 2021 at 09:21:41PM -0500, Olivier Dion via Guix-patches via wrote:
> For some reason, the build recently failed with:
> 
>         pfmlib_perf_event_pmu.c:349:36: error: ?%s? directive output may be truncated writing up to 255 bytes into a region of size between 0 and 4095 [-Werror=format-truncation=]
>           349 |   snprintf(d2path, MAXPATHLEN, "%s/%s", debugfs_mnt, d1->d_name);
>               |                                    ^~
>         pfmlib_perf_event_pmu.c:349:3: note: ?snprintf? output between 2 and 4352 bytes into a destination of size 4096
>           349 |   snprintf(d2path, MAXPATHLEN, "%s/%s", debugfs_mnt, d1->d_name);
>               |   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>         pfmlib_perf_event_pmu.c:399:58: error: ?%s? directive output may be truncated writing up to 255 bytes into a region of size between 0 and 4095 [-Werror=format-truncation=]
>           399 |                         snprintf(idpath, MAXPATHLEN, "%s/%s/id", d2path, d2->d_name);
>               |                                                          ^~
>         pfmlib_perf_event_pmu.c:399:25: note: ?snprintf? output between 5 and 4355 bytes into a destination of size 4096
>           399 |                         snprintf(idpath, MAXPATHLEN, "%s/%s/id", d2path, d2->d_name);
>               |                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>         cc1: all warnings being treated as errors
> 
> * gnu/packages/linux.scm (libpfm4): Fix build.
> (%standard-phases) Add `-Wno-format-truncation` to CFLAGS in build phase.

Thanks! Pushed as c7795eccaf432beec7366fa901b4bb6fc24cfead