how do I compile firefox with gcc3?

["Steven M. Bellovin" <smb%cs.columbia.edu@localhost>]

I need to compile firefox 1.5.0.5 on a -current machine; it's having
problems that may be related to gcc4:

c++ -o XFormsFunctionCall.o -c  -DMOZILLA_INTERNAL_API -DOSTYPE=\"NetBSD3.99\" -
DOSARCH=\"NetBSD\" -DBUILD_ID=0000000000  -I../../../../dist/include/string -I..
/../../../dist/include/xpcom -I../../../../dist/include/dom -I../../../../dist/i
nclude/content -I../../../../dist/include/widget -I../../../../dist/include/xpco
nnect -I../../../../dist/include/js -I../../../../dist/include/unicharutil -I../
../../../dist/include/layout -I../../../../dist/include/necko -I../../../../dist
/include/htmlparser -I../../../../dist/include/transformiix -I../../../../dist/i
nclude -I../../../../dist/include/nspr -I/usr/pkg/include -I/usr/pkg/include  -I
. -I./../base -I./../xml -I./../xml/dom -I./../xslt -I/usr/pkg/xorg/include   -f
PIC -DPIC  -I/usr/pkg/include -I/usr/include -I/usr/pkg/include/freetype2  -I/us
r/pkg/xorg/include -fno-rtti -fno-exceptions -Wall -Wconversion -Wpointer-arith 
-Wcast-align -Woverloaded-virtual -Wsynth -Wno-ctor-dtor-privacy -Wno-non-virtua
l-dtor -Wno-long-long -O2 -I/usr/pkg/include -I/usr/include -I/usr/pkg/include/f
reetype2 -Dunix -fshort-wchar -pthread -pipe  -DNDEBUG -DTRIMMED -O2  -I/usr/pkg
/include -I/usr/include -I/usr/pkg/include/freetype2  -I/usr/pkg/xorg/include -D
MOZILLA_CLIENT -include ../../../../mozilla-config.h -Wp,-MD,.deps/XFormsFunctio
nCall.pp XFormsFunctionCall.cpp
XFormsFunctionCall.cpp: In member function 'virtual nsresult XFormsFunctionCall:
:evaluate(txIEvalContext*, txAExprResult**)':
XFormsFunctionCall.cpp:116: warning: unused variable 'retvalue'
XFormsFunctionCall.cpp:137: warning: unused variable 'res'
XFormsFunctionCall.cpp:137: warning: unused variable 'test'
XFormsFunctionCall.cpp:225: error: cannot convert 'double (*)()' to 'double' in 
initialization
../../../../dist/include/xpcom/nsAutoPtr.h: In member function 'void** nsRefPtr<
T>::begin_assignment() [with T = txNodeSet]':
../../../../dist/include/xpcom/nsAutoPtr.h:1088:   instantiated from 'T** nsRefP
tr<T>::StartAssignment() [with T = txNodeSet]'
../../../../dist/include/xpcom/nsAutoPtr.h:1163:   instantiated from 'nsRefPtrGe
tterAddRefs<T>::operator T**() [with T = txNodeSet]'
XFormsFunctionCall.cpp:92:   instantiated from here
../../../../dist/include/xpcom/nsAutoPtr.h:913: warning: dereferencing type-punn
ed pointer will break strict-aliasing rules

Is there some way to make it use gcc3 for the compilation?

                --Steven M. Bellovin, http://www.cs.columbia.edu/~smb