travis-ci: Disable C++ optional objects on AArch64 container

travis-ci: Disable C++ optional objects on AArch64 container

Travis-CI seems to have enforced memory limit on containers,
and the 'GCC check-tcg' job started to fail on AArch64 [*]:

  [2041/3679] Compiling C++ object libcommon.fa.p/disas_nanomips.cpp.o
  FAILED: libcommon.fa.p/disas_nanomips.cpp.o
  {standard input}: Assembler messages:
  {standard input}:577781: Warning: end of file not at end of a line; newline inserted
  {standard input}:577882: Error: unknown pseudo-op: `.lvl35769'
  {standard input}: Error: open CFI at the end of file; missing .cfi_endproc directive
  c++: fatal error: Killed signal terminated program cc1plus
  compilation terminated.

Until we have a replacement for this job on Gitlab-CI, disable
compilation of C++ files by forcing the c++ compiler to /bin/false
so Meson build system can not detect it:

  $ ../configure --cxx=/bin/false

  Compilation
                       C compiler: cc
                  Host C compiler: cc
                     C++ compiler: NO

[*] https://travis-ci.org/github/qemu/qemu/jobs/757819402#L3754

Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Wainer dos Santos Moschetta <wainersm@redhat.com>
Message-Id: <20210207121239.2288530-1-f4bug@amsat.org>
Message-Id: <20210211122750.22645-8-alex.bennee@linaro.org>