--- bsd.gcc.mk.orig	2012-05-16 08:35:39.359670220 +0300
+++ bsd.gcc.mk	2012-05-16 08:47:40.709674341 +0300
@@ -5,6 +5,13 @@
 #
 # Created by: Edwin Groothuis <edwin@freebsd.org>
 #
+# For users:
+# if you would like to use GCC from ports as your ports compiler, you can
+# specify that with a WITH_GCC knob in your make.conf.
+#
+# Example:
+#	WITH_GCC=	4.6			# use GCC 4.6 to compile ports
+#
 # For port developers:
 # If your port needs a specific (minimum) version of GCC, you can easily
 # specify that with a "USE_GCC=" statement.  Unless absolutely necessary
@@ -26,6 +33,20 @@
 # Due to object file incompatiblity between Fortran compilers, we strongly
 # recommend to use only one of them on any system.
 #
+# Interaction between WITH_GCC user knob and USE_GCC port knob:
+# - if WITH_GCC is defined, but USE_GCC is not defined,
+#   then USE_GCC gets set from WITH_GCC
+# - if both are defined
+#  o if USE_GCC is a concrete version, then it wins
+#  o else (if USE_GCC has the "X+") form, then the minimum requested
+#    version becomes MAX(X, Y), where Y is from WITH_GCC;
+#    whether WITH_GCC has "Y" or "Y+" form doesn't matter in this case
+# In all cases WITH_GCC can be used only to increase minimum required
+# GCC version, unless a port wants a concrete fixed version.
+#
+# Note that the GCC ports and their dependencies are always built with
+# the base GCC to avoid circular dependencies and bootstrapping problems.
+#
 # If you are wondering what your port exactly does, use "make test-gcc"
 # to see some debugging.
 #
@@ -98,6 +119,30 @@
 MAKE_ENV+=		F77="${F77}" FC="${FC}" FFLAGS="${FFLAGS}"
 .endif
 
+.if defined(WITH_GCC) && ${PORTNAME} != gcc
+
+# See if we can use a later version or exclusively the one specified.
+_WITH_GCC:=	${WITH_GCC:S/+//}
+
+# Check if WITH_GCC points to a valid version.
+.for v in ${GCCVERSIONS}
+. for j in ${GCCVERSION_${v}}
+.  if ${_WITH_GCC}==${j}
+_WITH_GCCVERSION_OKAY=	true;
+.  endif
+. endfor
+.endfor
+
+.if !defined(_WITH_GCCVERSION_OKAY)
+IGNORE=	Unknown version of GCC specified (WITH_GCC=${WITH_GCC})
+.endif
+
+.if !defined(USE_GCC)
+USE_GCC:= ${WITH_GCC}
+.undef _WITH_GCC
+.endif
+
+.endif # WITH_GCC
 
 .if defined(USE_GCC)
 
@@ -143,6 +188,11 @@
 # get the first available version.
 #
 .if defined(_GCC_ORLATER)
+. if defined(_WITH_GCC)
+.  if ${_USE_GCC} < ${_WITH_GCC}
+_USE_GCC:= ${_WITH_GCC}
+.  endif
+. endif
 . for v in ${GCCVERSIONS}
 .  if ${_USE_GCC} == ${_GCCVERSION_${v}_V}
 _GCC_MIN1:=	true
@@ -180,22 +230,31 @@
 V:=			${_GCCVERSION_${v}_V:S/.//}
 _GCC_BUILD_DEPENDS:=	gcc${V}
 _GCC_PORT_DEPENDS:=	gcc${V}
+_GCC_OWN_DEPENDS!= (cd ${PORTSDIR}/lang/${_GCC_BUILD_DEPENDS} && ${MAKE} -V _UNIFIED_DEPENDS)
+.   for _CURDIR in ${.CURDIR} # only loop variable are expanded in variable modifiers
+.   if ${_GCC_OWN_DEPENDS:M*\:${_CURDIR}} != ""
+.undef _GCC_BUILD_DEPENDS
+.undef _GCC_PORT_DEPENDS
+.   else
 CC:=			gcc${V}
 CXX:=			g++${V}
 CPP:=			cpp${V}
-.   if ${_USE_GCC} != 3.4
+.    if ${_USE_GCC} != 3.4
 CFLAGS+=		-Wl,-rpath=${LOCALBASE}/lib/${_GCC_BUILD_DEPENDS}
 LDFLAGS+=		-Wl,-rpath=${LOCALBASE}/lib/${_GCC_BUILD_DEPENDS}
-.    if defined (USE_FORTRAN)
-.    if ${USE_FORTRAN} == yes
+.     if defined (USE_FORTRAN)
+.     if ${USE_FORTRAN} == yes
 FFLAGS+=		-Wl,-rpath=${LOCALBASE}/lib/${_GCC_BUILD_DEPENDS}
-.    endif
+.     endif
+.     endif
 .    endif
 .   endif
+.   endfor
 .  endif
 . endif
 .endfor
 .undef V
+.undef _GCC_OWN_DEPENDS
 
 .if defined(_GCC_BUILD_DEPENDS)
 BUILD_DEPENDS+=	${_GCC_PORT_DEPENDS}:${PORTSDIR}/lang/${_GCC_BUILD_DEPENDS}
--- bsd.port.mk.orig	2012-05-06 12:14:36.049668562 +0300
+++ bsd.port.mk	2012-05-06 11:56:45.909668044 +0300
@@ -1678,7 +1678,7 @@
 CONFIGURE_ENV+=	MAKE=${GMAKE}
 .endif
 
-.if defined(USE_GCC) || defined(USE_FORTRAN)
+.if defined(USE_GCC) || defined(USE_FORTRAN) || defined(WITH_GCC)
 .include "${PORTSDIR}/Mk/bsd.gcc.mk"
 .endif