configure: assembler stdout incorrect (cosmetic issue only)

[rhc54]

I'm seeing an incorrect identification of the hardware architecture (similar to issue reported on master #3032):

*** Assembler
checking dependency style of gcc... gcc3
checking for BSD- or MS-compatible name lister (nm)... /usr/bin/nm -B
checking the name lister (/usr/bin/nm -B) interface... BSD nm
checking for fgrep... /usr/bin/grep -F
checking if .proc/endp is needed... no
checking directive for setting text section... .text
checking directive for exporting symbols... .globl
checking for objdump... objdump
checking if .note.GNU-stack is needed... yes
checking suffix for labels... :
checking prefix for global symbol labels... 
checking prefix for lsym labels... .L
checking prefix for function in .type... @
checking if .size is needed... yes
checking if .align directive takes logarithmic value... no
checking if processor supports x86_64 16-byte compare-and-exchange... yes
checking if compiler correctly handles volatile 128bits... yes
checking if gcc supports GCC inline assembly... yes
checking if gcc supports DEC inline assembly... no
checking if gcc supports XLC inline assembly... no
checking for assembly format... default-.text-.globl-:--.L-@-1-0-1-1-1
checking for assembly architecture... AMD64
checking for builtin atomics... BUILTIN_NO
checking for pre-built assembly file... no (atomic-amd64-linux.s not found)
checking whether possible to generate assembly file... yes
checking for atomic assembly filename... atomic-local.s

This was on an Intel x86_64 box.

[jsquyres]

Per the discussion on #3039, this feels like a cosmetic issue, not something that is actually doing the Wrong Thing on the back-end. Defer to v2.1.1.