support/scripts/dependencies.sh: cleanup the output of the 32 bits gcc test

support/scripts/dependencies.sh: cleanup the output of the 32 bits gcc test

The screen is cluttered when we build for 32 bit target and 32 bit gcc
is missing.

  ~/buildroot$ make
  [...]
  /usr/bin/ld: cannot find crt1.o: No such file or directory
  /usr/bin/ld: cannot find crti.o: No such file or directory
  /usr/bin/ld: skipping incompatible /usr/lib/gcc/x86_64-linux-gnu/4.9/libgcc.a when searching for -lgcc
  /usr/bin/ld: cannot find -lgcc
  /usr/bin/ld: skipping incompatible /usr/lib/gcc/x86_64-linux-gnu/4.9/libgcc_s.so when searching for -lgcc_s
  /usr/bin/ld: cannot find -lgcc_s
  /usr/bin/ld: cannot find -lc
  /usr/bin/ld: skipping incompatible /usr/lib/gcc/x86_64-linux-gnu/4.9/libgcc.a when searching for -lgcc
  /usr/bin/ld: cannot find -lgcc
  /usr/bin/ld: skipping incompatible /usr/lib/gcc/x86_64-linux-gnu/4.9/libgcc_s.so when searching for -lgcc_s
  /usr/bin/ld: cannot find -lgcc_s
  /usr/bin/ld: cannot find crtn.o: No such file or directory
  collect2: error: ld returned 1 exit status
  [...]
  Your Buildroot configuration needs a compiler capable of building 32 bits binaries.

The final note is enough, and adding 2>/dev/null to the gcc test
invocation is also more consistent with the rest of the script. The
patch makes the '/usr/bin/ld:' and 'collect2:' lines go away.

Signed-off-by: Jens Stimpfle <debian@jstimpfle.de>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>