The 'mesa' package is failing to build on these experimental
paladins:
    edgar quawks reef sentry wizpig

The failure is seen first _only on reef_ in this run:
    https://uberchromegw.corp.google.com/i/chromeos/builders/reef-paladin/builds/3033
In that same run, the other four paladins built successfully.

In the previous run, all five paladins built successfully.

In the run following the first reef failure, all five paladins
showed the failure.

This appears to be the relevant error text from the mesa build
failure:
====
mesa-17.1.0-r12: Package libomxil-bellagio was not found in the pkg-config search path.
mesa-17.1.0-r12: Perhaps you should add the directory containing `libomxil-bellagio.pc'
mesa-17.1.0-r12: to the PKG_CONFIG_PATH environment variable
mesa-17.1.0-r12: No package 'libomxil-bellagio' found
mesa-17.1.0-r12: ./configure: line 22372: test: : integer expression expected
mesa-17.1.0-r12: ./configure: line 22378: test: : integer expression expected
mesa-17.1.0-r12: configure: error: LLVM 3.3.0 or newer is required for gallium
mesa-17.1.0-r12: 
mesa-17.1.0-r12: !!! Please attach the following file when seeking support:
mesa-17.1.0-r12: !!! /build/reef/tmp/portage/media-libs/mesa-17.1.0-r12/work/mesa-17.1.0/config.log
mesa-17.1.0-r12:  * ERROR: media-libs/mesa-17.1.0-r12::chromiumos failed (configure phase):
mesa-17.1.0-r12:  *   econf failed
====

At this time, no canary has started since the failure, so it's not known
whether this problem is peculiar to the builders or to the boards.  The
expectation is that the canaries and PFQs will fail in the same way.

Passing to the sheriff for action.