jimtcl: fix sparc64 compile

It is general safe to use -fPIC for all architectures.
-fpic breaks sparc64 compile.

Generally gcc just optimize position independent code
for m68k, powerpc and sparc with -fpic.
The size differences are minimal, f.e. for powerpc:
   text    data     bss     dec     hex filename
 235983    5336     684  242003   3b153 output/target/usr/lib/libjim.0.75
 236255    8456     684  245395   3be93 output/target/usr/lib/libjim.so.0.75

So instead of keeping special settings for sparc64 it would be better
to always use -fPIC in general.

Runtime tested on Qemu ARM, MIPS, PPC and SPARC64.
Fixes:
http://autobuild.buildroot.net/results/98f391ad13f22828c022f185c0166daabdb4c1ad/



[Peter: tweak comment as suggested by Thomas]
Signed-off-by: Waldemar Brodkorb <wbx@openadk.org>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>