Merge remote-tracking branch 'origin/maint'

* origin/maint:
  glr.cc: fix a clang warning
  maint: update copyright years
  build: fix VPATH issue
  build: avoid clang's colored diagnostics in the test suite
  tests: please clang and use ".cc", not ".c", for C++ input
  gnulib: update
  skeletons: avoid empty switch constructs
  lalr1.cc: fix compiler warnings
  yacc.c: do not use __attribute__ unprotected
  tests: style changes

THANKS

@@ -107,6 +107,7 @@ Ralf Wildenhues           Ralf.Wildenhues@gmx.de
 Richard Stallman          rms@gnu.org
 Rob Vermaas               rob.vermaas@gmail.com
 Robert Anisko             anisko_r@epita.fr
+Rob Conde                 rob.conde@ai-solutions.com
 Roland Levillain          roland@lrde.epita.fr
 Satya Kiran Popuri        satyakiran@gmail.com
 Sebastian Setzer          sebastian.setzer.ext@siemens.com
@@ -127,6 +128,7 @@ Tommy Nordgren            tommy.nordgren@chello.se
 Troy A. Johnson           troyj@ecn.purdue.edu
 Tys Lefering              gccbison@gmail.com
 Valentin Tolmer           nitnelave1@gmail.com
+Victor Khomenko           victor.khomenko@newcastle.ac.uk
 Vin Shelton               acs@alumni.princeton.edu
 W.C.A. Wijngaards         wouter@NLnetLabs.nl
 Wayne Green               wayne@infosavvy.com