guix: use -fcommon when building glibc 2.24

GCC 10 started using -fno-common by default, which causes issues with
the powerpc builds using gibc 2.24. A patch was commited to glibc to fix
the issue, 18363b4f010da9ba459b13310b113ac0647c2fcc but is non-trvial
to backport, and was broken in at least one way, see the followup in
commit 7650321ce037302bfc2f026aa19e0213b8d02fe6.

For now, retain the legacy GCC behaviour by passing -fcommon when
building glibc 2.24.

https://gcc.gnu.org/onlinedocs/gcc/Code-Gen-Options.html.
https://sourceware.org/git/?p=glibc.git;a=commit;h=18363b4f010da9ba459b13310b113ac0647c2fcc
https://sourceware.org/git/?p=glibc.git;a=commit;h=7650321ce037302bfc2f026aa19e0213b8d02fe6

contrib/guix/manifest.scm

@@ -537,7 +537,8 @@ inspecting signatures in Mach-O binaries.")
               (patches (search-our-patches "glibc-ldd-x86_64.patch"
                                            "glibc-versioned-locpath.patch"
                                            "glibc-2.24-elfm-loadaddr-dynamic-rewrite.patch"
-                                           "glibc-2.24-no-build-time-cxx-header-run.patch"))))))
+                                           "glibc-2.24-no-build-time-cxx-header-run.patch"
+                                           "glibc-2.24-fcommon.patch"))))))
 
 (define-public glibc-2.27/bitcoin-patched
   (package

contrib/guix/patches/glibc-2.24-fcommon.patch

@@ -0,0 +1,32 @@
+commit 264a4a0dbe1f4369db315080034b500bed66016c
+Author: fanquake <fanquake@gmail.com>
+Date:   Fri May 6 11:03:04 2022 +0100
+
+    build: use -fcommon to retain legacy behaviour with GCC 10
+    
+    GCC 10 started using -fno-common by default, which causes issues with
+    the powerpc builds using gibc 2.24. A patch was commited to glibc to fix
+    the issue, 18363b4f010da9ba459b13310b113ac0647c2fcc but is non-trvial
+    to backport, and was broken in at least one way, see the followup in
+    commit 7650321ce037302bfc2f026aa19e0213b8d02fe6.
+    
+    For now, retain the legacy GCC behaviour by passing -fcommon when
+    building glibc.
+    
+    https://gcc.gnu.org/onlinedocs/gcc/Code-Gen-Options.html.
+    https://sourceware.org/git/?p=glibc.git;a=commit;h=18363b4f010da9ba459b13310b113ac0647c2fcc
+    https://sourceware.org/git/?p=glibc.git;a=commit;h=7650321ce037302bfc2f026aa19e0213b8d02fe6
+
+diff --git a/Makeconfig b/Makeconfig
+index ee379f5852..63c4a2f234 100644
+--- a/Makeconfig
++++ b/Makeconfig
+@@ -824,7 +824,7 @@ ifeq	"$(strip $(+cflags))" ""
+ +cflags	:= $(default_cflags)
+ endif	# $(+cflags) == ""
+ 
+-+cflags += $(cflags-cpu) $(+gccwarn) $(+merge-constants) $(+math-flags)
+++cflags += $(cflags-cpu) $(+gccwarn) $(+merge-constants) $(+math-flags) -fcommon
+ +gcc-nowarn := -w
+ 
+ # Don't duplicate options if we inherited variables from the parent.