build macros: add _legacy_common_support macro for adding -fcommon to compiler flags

Since version 10, gcc defaults to '-fno-common':
https://gcc.gnu.org/gcc-10/porting_to.html#common

Builds may fail with 'multiple definition of ...' errors. As a short term
workaround for such failure, it is possible to add '-fcommon' to the flags
by defining  '%_legacy_common_support'.

%define _legacy_common_support 1

Properly fixing the failure is always preferred!

2 files changed, 2 insertions, 2 deletions

diff --git a/NEWS b/NEWS
index 6d27add..cd60c11 100644
--- a/NEWS
+++ b/NEWS
@@ -1,4 +1,4 @@
-
+- build macros: add _legacy_common_support macro for adding -fcommon to compiler flags
 - build.macros: run /usr/lib/rpm/check-buildroot at end of %install scriptlet
   via __arch_install_post
 
diff --git a/build.macros.in b/build.macros.in
index 07f4364..7a15019 100644
--- a/build.macros.in
+++ b/build.macros.in
@@ -192,7 +192,7 @@ GCONF_CONFIG_SOURCE=`%{_gconftool_bin} --get-default-source` %{_gconftool_bin} -
 %Werror_cflags -Wformat -Werror=format-security
 
 %_ssp_cflags -fstack-protector --param=ssp-buffer-size=4%{?_serverbuild_flags: %_serverbuild_flags}
-%__common_cflags -O2 %{debugcflags} -pipe %{Werror_cflags} %{?_fortify_cflags}
+%__common_cflags -O2 %{debugcflags} -pipe %{Werror_cflags} %{?_fortify_cflags}%{?_legacy_common_support: -fcommon}
 %__common_cflags_with_ssp %{__common_cflags} %{?_ssp_cflags}
 
 # Servers opt flags.