CC messed up in RELENG_7 build

[Dominic Fandrey]

The sources were csupped ~3 hours ago. My CC is defined as follows:
env CCACHE_PREFIX=/usr/local/bin/distcc /usr/local/bin/ccache cc

I have done many buildworld, buildkernel and port builds with this setting and
it never caused any problems. However today buildworld fails the following way:

env CCACHE_PREFIX=/usr/local/bin/distcc /usr/local/bin/ccache env CCACHE_PREFIX=/usr/local/bin/distcc /usr/local/bin/ccache cc -m32 -march=k8 -mfancy-math-387 -DCOMPAT_32BIT  -iprefix /usr/obj/6510b/amd64/usr/src/lib32/usr/  -L/usr/obj/6510b/amd64/usr/src/lib32/usr/lib32  -B/usr/obj/6510b/amd64/usr/src/lib32/usr/lib32 -c -O2 -fno-strict-aliasing -pipe -DIN_GCC -DIN_LIBGCC2 -D__GCC_FLOAT_NOT_NEEDED  -DHAVE_GTHR_DEFAULT  -I/usr/src/gnu/lib/libgcc/../../../contrib/gcclibs/include  -I/usr/src/gnu/lib/libgcc/../../../contrib/gcc/config -I/usr/src/gnu/lib/libgcc/../../../contrib/gcc -I.  -I/usr/src/gnu/lib/libgcc/../../usr.bin/cc/cc_tools  -fvisibility=hidden -DHIDE_EXPORTS -fPIC  -DL_muldi3 -o _muldi3.o /usr/src/gnu/lib/libgcc/../../../contrib/gcc/libgcc2.c
distcc[76450] (main) CRITICAL! distcc seems to have invoked itself recursively!
distcc[76449] (main) CRITICAL! distcc seems to have invoked itself recursively!
distcc[76448] ERROR: compile /usr/src/gnu/lib/libgcc/../../../contrib/gcc/libgcc2.c on localhost failed with exit code 111
*** Error code 111
1 error
*** Error code 2
1 error
*** Error code 2
1 error
*** Error code 2
1 error
*** Error code 2

Stop in /usr/src.



It looks to me like there has been some kind of recursive substitution of CC,
turning
env CCACHE_PREFIX=/usr/local/bin/distcc /usr/local/bin/ccache cc
into
env CCACHE_PREFIX=/usr/local/bin/distcc /usr/local/bin/ccache env CCACHE_PREFIX=/usr/local/bin/distcc /usr/local/bin/ccache cc

I have looked at the involved Makefile.in files, but I didn't find anything that
looked suspicious to me.