need to define _ISOC99_SOURCE

[Paul Eggert]

   From: Akim Demaille <akim@epita.fr>
   Date: 31 Jul 2000 17:53:03 +0200

   | And _HPUX_SOURCE ? I'd like to compile GNU packages with "cc -Aa"
   | instead of "cc -Aa -D_HPUX_SOURCE" on HP-UX.

   I was just waiting for someone to tell me it was that simple :)

Unfortunately, it's not that simple.  In HP-UX 10.20, one should
compile with "-Ae" and not with "-Aa -D_HPUX_SOURCE", as only -Ae
supports 64-bit integral types.

GNU tar 1.13.17 redefines AM_PROG_CC_STDC to try C compiler options in
the following order:

	[nothing]
	-qlanglvl=ansi
	-std1
	-Ae
	-Aa -D_HPUX_SOURCE
	-Xc -D__EXTENSIONS__

Presumably this check should find its way into autoconf, merged into
the check that I wrote about in my previous message.