buildflags.md: Mention optional -fcommon under compiler flags

From Fedora commit ac57cc99aa.

Related: #2005080
This commit is contained in:
Florian Weimer 2021-11-15 15:26:05 +01:00
parent 739df788ba
commit 4ca70eae08

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@ -235,6 +235,8 @@ The general (architecture-independent) build flags are:
* `-grecord-gcc-switches`: Include select GCC command line switches in
the DWARF debugging information. This is useful for detecting the
presence of certain build flags and general hardening coverage.
* `-fcommon`: This optional flag is used to build legacy software
which relies on C tentative definitions. It is disabled by default.
For hardened builds (which are enabled by default, see above for how
to disable them), the flag