It seems to build OK on my Solaris 10, try the following:

Save the file below as /usr/pkg/etc/mk.conf
You may need to adjust your DISTDIR, PKG_DBDIR, and optimisation flags, etc

WRKOBJDIR=/usr/obj.pkg
PACKAGES=/usr/packages
DISTDIR=/usr/distfiles
PKG_DBDIR=/usr/pkg/db/pkg
LOCALBASE=/usr/pkg
FETCH_CMD=/usr/pkg/bin/ftp
PAX=/usr/pkg/bin/pax
SED=/usr/pkg/bin/nbsed

DEPENDS_TARGET=package
UPDATE_TARGET=package

GCC_REQD+=3
USE_PKGSRC_GCC=yes

OPTIM_FLAGS=-mcpu=ultrasparc -O2

.ifdef BSD_PKG_MK
COPTS+=${OPTIM_FLAGS}
CFLAGS+=${OPTIM_FLAGS}
CXXFLAGS+=${OPTIM_FLAGS}
.else
COPTS+=${OPTIM_FLAGS}
.endif


Do 'rm -rf' on the pkgsrc tree and then do fresh 'cvs checkout'

PATH=/usr/pkg/bin:/usr/pkg/sbin:/usr/pkg/gcc3/bin:/usr/bin:/usr/sbin:/usr/ccs/bin
export PATH

Then try building MesaLib again.