sawman: Link using gcc instead of ld

Using ld may cause a link failure due to using the default emulation
linker which is configured when building the linker in binutils.  Using
gcc instead will pass the appropriate -m value because the compiler
knows the ABI you are using.

Here is an example of the failure:

ld: .libs/libdirectfbwm_sawman.a.tmp/sawman_wm.o: ABI is incompatible
with that of the selected emulation
ld: failed to merge target specific data of file
.libs/libdirectfbwm_sawman.a.tmp/sawman_wm.o
ld: Attempt to do relocatable link with elf64-tradbigmips input and
elf32-tradbigmips output
ld: .libs/libdirectfbwm_sawman.a.tmp/sawman_wm.o: file class ELFCLASS64
incompatible with ELFCLASS32
ld: final link failed: File in wrong format

Fixes:

   http://autobuild.buildroot.net/results/e4b/e4b77681a44626efa2a44627604630697e785086/



Signed-off-by: Vicente Olivert Riera <Vincent.Riera@imgtec.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>