Don't include sys/param.h

Don't include sys/param.h

sys/param.h on recent versions of powerpc glibc ends up including
asm/elf.h via asm/sigcontex.h.  asm/elf.h defines R_PPC_* and R_PPC64_*
macros, which clash with our include/elf/ppc.h and include/elf/ppc64.h.
It turns out that no current source uses LD_PATHMAX, so there is no
need for limits.h or sys/param.h, except for one occurrence of UINT_MAX.
I don't have a quarrel with limits.h, but it seems unnecessary just
for UINT_MAX.

	* sysdep.h: Don't include limits.h and sys/param.h.  Don't
	include unistd.h twice.
	(LD_PATHMAX): Don't define.
	* ldlang.c (lang_common): Don't use UINT_MAX.