build: pass -fcommon when building genisoimage
5da31f57d807
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Description

build: pass -fcommon when building genisoimage

Summary:
Starting with the 10.1 release, GCC defaults to -fno-common. This causes
linking issues when building genisoimage:

bash
[ 98%] Building C object
genisoimage/CMakeFiles/genisoimage.dir/checksum.o
[100%] Linking C executable genisoimage
/usr/bin/ld: CMakeFiles/genisoimage.dir/apple.o:(.bss+0x0): multiple
definition of `outfile';
CMakeFiles/genisoimage.dir/genisoimage.o:(.bss+0x0): first defined here
/usr/bin/ld: CMakeFiles/genisoimage.dir/boot.o:(.bss+0x0): multiple
definition of `outfile';
CMakeFiles/genisoimage.dir/genisoimage.o:(.bss+0x0): first defined here
/usr/bin/ld: CMakeFiles/genisoimage.dir/desktop.o:(.bss+0x0): multiple
definition of `outfile';
CMakeFiles/genisoimage.dir/genisoimage.o:(.bss+0x0): first defined here
/usr/bin/ld: CMakeFiles/genisoimage.dir/dvd_file.o:(.bss+0x0): multiple
definition of `outfile';
CMakeFiles/genisoimage.dir/genisoimage.o:(.bss+0x0): first defined here

Rather than patching genisoimage further, pass -fcommon to preserve the
legacy GCC behaviour.

Backport of core PR19553.
Fixes the OSX depends build on Arch.

Test Plan: