[oe] mesa-gl build failing for RPi0

[Scott Ellis]

Using rocko

...
| glsl/.libs/libstandalone.a(libmesautil_la-disk_cache.o): In function `evict_lru_item':
| /usr/src/debug/mesa-gl/2_17.1.7-r0/mesa-17.1.7/src/util/disk_cache.c:615: undefined reference to `__atomic_fetch_add_8'
| glsl/.libs/libstandalone.a(libmesautil_la-disk_cache.o): In function `cache_put':
| /usr/src/debug/mesa-gl/2_17.1.7-r0/mesa-17.1.7/src/util/disk_cache.c:886: undefined reference to `__atomic_fetch_add_8'
| glsl/.libs/libstandalone.a(libmesautil_la-disk_cache.o): In function `disk_cache_remove':
| /usr/src/debug/mesa-gl/2_17.1.7-r0/mesa-17.1.7/src/util/disk_cache.c:637: undefined reference to `__atomic_fetch_add_8'
| collect2: error: ld returned 1 exit status
| Makefile:2076: recipe for target 'glsl_compiler' failed
| make[4]: *** [glsl_compiler] Error 1
| make[4]: Leaving directory '/oe4/rocko/tmp-rocko/work/arm1176jzfshf-vfp-poky-linux-gnueabi/mesa-gl/2_17.1.7-r0/build/src/compiler'
| Makefile:1528: recipe for target 'all' failed
| make[3]: *** [all] Error 2
| make[3]: Leaving directory '/oe4/rocko/tmp-rocko/work/arm1176jzfshf-vfp-poky-linux-gnueabi/mesa-gl/2_17.1.7-r0/build/src/compiler'
| Makefile:840: recipe for target 'all-recursive' failed
| make[2]: *** [all-recursive] Error 1
| make[2]: Leaving directory '/oe4/rocko/tmp-rocko/work/arm1176jzfshf-vfp-poky-linux-gnueabi/mesa-gl/2_17.1.7-r0/build/src'
| Makefile:631: recipe for target 'all' failed
| make[1]: *** [all] Error 2
| make[1]: Leaving directory '/oe4/rocko/tmp-rocko/work/arm1176jzfshf-vfp-poky-linux-gnueabi/mesa-gl/2_17.1.7-r0/build/src'
| Makefile:631: recipe for target 'all-recursive' failed
| make: *** [all-recursive] Error 1
| ERROR: oe_runmake failed


The solution used for armv5 boards in mesa.inc works for armv6

  CFLAGS_append_armv6 = " -DMISSING_64BIT_ATOMICS"


I'm using it in a private layer bbappend, but might belong
in mesa.inc alongside the armv5 line.


Some discussion of the bug here

  https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=874531