package/gdb: fix gnulib issue with musl and uClibc toolchains again

package/gdb: fix gnulib issue with musl and uClibc toolchains again

The commit [1] doesn't fix this issue for all cases (it doesn't work
when BR2_PACKAGE_GDB_DEBUGGER=y).
So, leave the configure script alone and override
gl_cv_func_gettimeofday_clobber from GDB_MAKE_ENV.

[1] 560334bb2a46a77081a3944d092df7732dfca432

Fixes:
http://autobuild.buildroot.net/results/719/719a441421030b79c0aa1bbfb707130f3ac87338

Signed-off-by: Romain Naour <romain.naour@gmail.com>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>