https://bugs.gentoo.org/705730

gcc-10 enabled f-no-common by default. Broke syslinux linking.
--- a/mk/com32.mk
+++ b/mk/com32.mk
@@ -47,6 +47,7 @@ GCCOPT += $(call gcc_ok,-falign-functions=0,-malign-functions=0)
 GCCOPT += $(call gcc_ok,-falign-jumps=0,-malign-jumps=0)
 GCCOPT += $(call gcc_ok,-falign-labels=0,-malign-labels=0)
 GCCOPT += $(call gcc_ok,-falign-loops=0,-malign-loops=0)
+GCCOPT += $(call gcc_ok,-fcommon)
 
 ifeq ($(FWCLASS),EFI)
 GCCOPT += -mno-red-zone
--- a/mk/elf.mk
+++ b/mk/elf.mk
@@ -42,6 +42,7 @@ GCCOPT += $(call gcc_ok,-falign-functions=0,-malign-functions=0)
 GCCOPT += $(call gcc_ok,-falign-jumps=0,-malign-jumps=0)
 GCCOPT += $(call gcc_ok,-falign-labels=0,-malign-labels=0)
 GCCOPT += $(call gcc_ok,-falign-loops=0,-malign-loops=0)
+GCCOPT += $(call gcc_ok,-fcommon)
 
 com32 = $(topdir)/com32
 core = $(topdir)/core
--- a/mk/embedded.mk
+++ b/mk/embedded.mk
@@ -51,6 +51,7 @@ GCCOPT    += $(call gcc_ok,-falign-jumps=0,-malign-jumps=0)
 GCCOPT    += $(call gcc_ok,-falign-labels=0,-malign-labels=0)
 GCCOPT    += $(call gcc_ok,-falign-loops=0,-malign-loops=0)
 GCCOPT    += $(call gcc_ok,-fvisibility=hidden)
+GCCOPT    += $(call gcc_ok,-fcommon)
 
 LIBGCC    := $(shell $(CC) $(GCCOPT) --print-libgcc)
 
--- a/mk/lib.mk
+++ b/mk/lib.mk
@@ -28,6 +28,7 @@ GCCOPT += $(call gcc_ok,-falign-functions=0,-malign-functions=0)
 GCCOPT += $(call gcc_ok,-falign-jumps=0,-malign-jumps=0)
 GCCOPT += $(call gcc_ok,-falign-labels=0,-malign-labels=0)
 GCCOPT += $(call gcc_ok,-falign-loops=0,-malign-loops=0)
+GCCOPT += $(call gcc_ok,-fcommon)
 
 INCLUDE	= -I$(SRC)
 STRIP	= strip --strip-all -R .comment -R .note
--- a/mk/efi.mk
+++ b/mk/efi.mk
@@ -7,7 +7,7 @@ core = $(topdir)/core
 # Set up architecture specifics; for cross compilation, set ARCH as apt
 # gnuefi sets up architecture specifics in ia32 or x86_64 sub directories
 # set up the LIBDIR and EFIINC for building for the appropriate architecture
-GCCOPT := $(call gcc_ok,-fno-stack-protector,)
+GCCOPT := $(call gcc_ok,-fno-stack-protector,) $(call gcc_ok,-fcommon)
 EFIINC = $(objdir)/include/efi
 LIBDIR  = $(objdir)/lib