10.0-CURRENT #0 r249720: graphics/jasper: eval: _at_CC_at_: not found

Trying to update port graphics/jasper on our FreeBSD 10.0-CURRENT boxes
(all r249720 or higher) fails on all(!) Core2Duo based systems (Intel
E8400 or Q6600) (CLANG 3.3) with the below shown error.

Interestingly, the port does compile on all boxes running the very same
FreeBSD 10.0-CURRENT with either Sandy-Bridge-E (i7-3939K) or Ivy Bridge
(i3-3220) CPUs. All systems have in common that I compile world and
kernel with option -O3 (CLANG 3.3), -march=native.
I also use the very same /etc/src.conf on all boxes:

WITH_CLANG_EXTRAS=      YES
WITH_LLVM=              YES
WITH_LLVM_EXTRAS=       YES
#
WITH_BIND_LIBS=         YES
WITH_BIND_SIGCHASE=     YES
WITH_BIND_LARGE_FILE=   YES
#
WITH_IDEA=              YES
#
#WITH_ICONV=            YES
#WITH_BSD_GREP=         YES
WITH_BSD_SORT=          YES
WITH_BSDCONFIG=         YES
WITH_BSD_PATCH=         YES
#
#WITH_OFED=             YES
WITH_NAND=              YES
WITH_NMTREE=            YES
#WITH_BMAKE=            YES
#WITH_CTF=              YES
#
MALLOC_PRODUCTION=      YES


I guess I hit a miscompilation with either option -O3 -march=native on
"Penryn" architectures with the new CLANG 3.3 compiler?

(By the way, I also see this obscure "_at_CC_at_: not found" error in
compiling games/qstat and it hits also the Core2Duo boxes, but not any
CPU type beyond the C2D).

Error compiling port graphics/jasper:

===>  Building for jasper-1.900.1_12
Making all in src
Making all in libjasper
Making all in include
Making all in jasper
/usr/bin/make  all-am
Making all in base
if /bin/sh /usr/local/bin/libtool --tag=CC --mode=compile _at_CC_at_
-DHAVE_CONFIG_H  -I. -I. -I../../../src/libjasper/include/jasper
-I../../../src/libjasper/include  -I/usr/local/include   -O2 -pipe -O3
-march=native -fno-strict-aliasing -MT jas_cm.lo -MD -MP -MF
".deps/jas_cm.Tpo" -c -o jas_cm.lo jas_cm.c;  then mv -f
".deps/jas_cm.Tpo" ".deps/jas_cm.Plo"; else rm -f ".deps/jas_cm.Tpo";
exit 1; fi
libtool: compile:  _at_CC_at_ -DHAVE_CONFIG_H -I. -I.
-I../../../src/libjasper/include/jasper -I../../../src/libjasper/include
-I/usr/local/include -O2 -pipe -O3 -march=native -fno-strict-aliasing
-MT jas_cm.lo -MD -MP -MF .deps/jas_cm.Tpo -c jas_cm.c  -fPIC -DPIC
-o .libs/jas_cm.o
eval: _at_CC_at_: not found
*** [jas_cm.lo] Error code 1

Stop
in /usr/ports/graphics/jasper/work/jasper-1.900.1/src/libjasper/base.
*** [all-recursive] Error code 1

Stop in /usr/ports/graphics/jasper/work/jasper-1.900.1/src/libjasper.
*** [all-recursive] Error code 1

Stop in /usr/ports/graphics/jasper/work/jasper-1.900.1/src.
*** [all-recursive] Error code 1

Stop in /usr/ports/graphics/jasper/work/jasper-1.900.1.
*** [do-build] Error code 1

Stop in /usr/ports/graphics/jasper.
*** [build] Error code 1

Stop in /usr/ports/graphics/jasper.

===>>> make failed for graphics/jasper
===>>> Aborting update

===>>> Killing background jobs