Why does postgres install try to use cc instead of gcc when compiling tcl ?

I use gcc and I have put the following line before ./configure

env CC=/opt/sfw/bin/gcc ./configure [...]

postgres install uses gcc most of the time but
when installing tcl it tries to use cc which is not properly installed
and the installation fails

how to overcome this problem ?

thanks for any help

hr

---------- message at the end of the compilation process
-------------------------

gmake[4]: Leaving directory
`/usr/local/download/postgresql/postgresql-7.2.3/src/pl/plpgsql/src'
gmake[3]: Leaving directory
`/usr/local/download/postgresql/postgresql-7.2.3/src/pl/plpgsql'
gmake[3]: Entering directory
`/usr/local/download/postgresql/postgresql-7.2.3/src/pl/tcl'
/bin/sh mkMakefile.tcldefs.sh '/usr/local/ActiveTcl/lib/tclConfig.sh'
'Makefile.tcldefs'
gmake[3]: Leaving directory
`/usr/local/download/postgresql/postgresql-7.2.3/src/pl/tcl'
gmake[3]: Entering directory
`/usr/local/download/postgresql/postgresql-7.2.3/src/pl/tcl'
cc -O -KPIC -I../../../src/include -I/opt/sfw/include
-I/usr/local/ActiveTcl/include -DHAVE_UNISTD_H=1 -DHAVE_LIMITS_H=1
-DTCL_WIDE_INT_TYPE=long\ long -DHAVE_STRUCT_DIRENT64=1
-DHAVE_STRUCT_STAT64=1 -DHAVE_TYPE_OFF64_T=1 -DWORDS_BIGENDIAN=1
-DHAVE_GETCWD=1 -DHAVE_OPENDIR=1 -DHAVE_STRSTR=1 -DHAVE_STRTOL=1
-DHAVE_STRTOLL=1 -DHAVE_STRTOULL=1 -DHAVE_TMPNAM=1 -DHAVE_WAITPID=1
-DHAVE_UNISTD_H=1 -DHAVE_SYS_PARAM_H=1 -DUSE_TERMIOS=1
-DHAVE_SYS_TIME_H=1 -DTIME_WITH_SYS_TIME=1 -DHAVE_TZNAME=1
-DHAVE_GMTIME_R=1 -DHAVE_LOCALTIME_R=1 -DHAVE_TIMEZONE_VAR=1
-DHAVE_ST_BLKSIZE=1 -Dstrtod=fixstrtod -DSTDC_HEADERS=1
-Dsocklen_t=unsigned -DNO_UNION_WAIT=1 -DHAVE_SIGNED_CHAR=1
-DHAVE_LANGINFO=1 -D_REENTRANT=1 -D_POSIX_PTHREAD_SEMANTICS=1
-DHAVE_SYS_IOCTL_H=1 -DHAVE_SYS_FILIO_H=1 -c -o pltcl.o pltcl.c
/usr/ucb/cc: language optional software package not installed
gmake[3]: *** [pltcl.o] Error 1
gmake[3]: Leaving directory
`/usr/local/download/postgresql/postgresql-7.2.3/src/pl/tcl'
gmake[2]: *** [all] Error 2
gmake[2]: Leaving directory
`/usr/local/download/postgresql/postgresql-7.2.3/src/pl'
gmake[1]: *** [all] Error 2
gmake[1]: Leaving directory
`/usr/local/download/postgresql/postgresql-7.2.3/src'
gmake: *** [all] Error 2