Followup on AIX issues - large file support

[Orion Poplawski]

Recent versions of amanda do not determine large file support flags 
properly when using GCC on AIX.  configure.in specifies the following 
getconf option to determine the required flags:

 *-ibm-aix*)
                       GETCONF_LFS="XBS5_ILP32_OFFBIG"
However, the values returned by getconf are valid only for the AIX C 
compiler, not GCC:

checking for large file compilation CFLAGS... -q32 -D_LARGE_FILES -qlonglong
checking for large file compilation LDFLAGS... -b32
checking for large file compilation LIBS... -lc -lpthread -lm
I'm not terribly familiar with autoconf, but it seems there should be at 
least a test to see if GCC is being used and not define GETCONF_LFS as 
above if it is.

However, this means that large file support is disabled in AIX w/GCC.   
I looked into using the builtin autoconf macro AC_SYS_LARGEFILE, but 
this does not appear to support AIX w/ the native compiler, though it 
seems to be the way to move in the future.

BTW, similar LFS flag definition exists for HP so there might be similar 
issues on that platform.

- Orion