Compile errors with SunPro CC + Fix

[Patrick Stach]

Bash version: 2.05b
OS and hardware: Solaris SPARC
Compiler: SunPro CC

make failed for lib/malloc/malloc.c due to the lack of
a return after the free_return: label in internal_free()
function.

Add a return; line at the end of the function and it goes away.

Thanks,
-Patrick Stach