Build failure textproc/icu on Solaris 10 x86 with SunStudio compiler

[Ibraheem Saleh <shadowhawk100%gmail.com@localhost>]

I'm trying to build textproc/icu on Solaris 10 x86 with the SunStudio
compiler and am stumped by this error:

generating dependency information for putil.cpp
"/usr/include/sys/feature_tests.h", line 342: Error: #error "Compiler
or options invalid; UNIX 03 and POSIX.1-2001 applications require the
use of c99".
generating dependency information for errorcode.cpp
generating ../common/svchook.mk
cd .. \
 && CONFIG_FILES=common/Makefile CONFIG_HEADERS= /usr/pkg/bin/pdksh
./config.status
config.status: creating common/Makefile
gmake[1]: Leaving directory `/pkgsrc/textproc/icu/work/icu/source/common'
gmake[1]: Entering directory `/pkgsrc/textproc/icu/work/icu/source/common'
CC -I/usr/include   -DU_HAVE_ELF_H=1 -DU_HAVE_ATOMIC=0  -I.
"-DDEFAULT_ICU_PLUGINS=\"/usr/pkg/lib/icu\" "
-DU_ATTRIBUTE_DEPRECATED= -DU_COMMON_IMPLEMENTATION  -O2
-I/usr/include -mt   -c -DPIC -KPIC -o errorcode.o errorcode.cpp
CC -I/usr/include   -DU_HAVE_ELF_H=1 -DU_HAVE_ATOMIC=0  -I.
"-DDEFAULT_ICU_PLUGINS=\"/usr/pkg/lib/icu\" "
-DU_ATTRIBUTE_DEPRECATED= -DU_COMMON_IMPLEMENTATION  -O2
-I/usr/include -mt   -c -DPIC -KPIC -o putil.o putil.cpp
"/usr/include/sys/feature_tests.h", line 342: Error: #error "Compiler
or options invalid; UNIX 03 and POSIX.1-2001 applications require the
use of c99".
gmake[1]: *** [putil.o] Error 2
gmake[1]: Leaving directory `/pkgsrc/textproc/icu/work/icu/source/common'
gmake: *** [all-recursive] Error 2
*** Error code 2

Stop.
bmake: stopped in /pkgsrc/textproc/icu
*** Error code 1

Stop.
bmake: stopped in /pkgsrc/textproc/icu

I see that patch-configure mentions needing c99 still on Solaris but
don't understand what needs to be done to fix this.

Does anybody know what might be causing this issue?

Thanks!