stringinfo.c compile error

My system is a standard Solaris 8 (Intel) environment.
please help me !

./configure --enable-multibyte --with-odbc

gmake
.........
stringinfo.c: In function `appendStringInfo':
stringinfo.c:104: `va_list' undeclared (first use in this function)
stringinfo.c:104: (Each undeclared identifier is reported only once
stringinfo.c:104: for each function it appears in.)
stringinfo.c:104: parse error before `args'
stringinfo.c:121: warning: implicit declaration of function `va_start'
stringinfo.c:121: `args' undeclared (first use in this function)
stringinfo.c:124: warning: implicit declaration of function `va_end'
gmake[2]: *** [stringinfo.o] Error 1
gmake[2]: Leaving directory `/usr/share/src/pgsql/src/backend/lib'
gmake[1]: *** [lib.dir] Error 2
gmake[1]: Leaving directory `/usr/share/src/pgsql/src/backend'
gmake: *** [all] Error 2.

version
postregesql 7.0.2
gcc : 2.95.2
gmake : 3.78.1
flex : 2.5.4

my path
PATH=/usr/sbin:/usr/bin:/usr/ccs/bin:/opt/sfw/bin