Cross compiling with --enable-ccache does not work

[alexcrichton]

If you enable ccache when doing a cross compile, you get this error:

$ make VERBOSE=1    
cfg: build triple x86_64-unknown-linux-gnu
cfg: host triples i686-unknown-linux-gnu x86_64-unknown-linux-gnu
cfg: target triples i686-unknown-linux-gnu x86_64-unknown-linux-gnu
cfg: non-build host triples i686-unknown-linux-gnu
cfg: non-build target triples i686-unknown-linux-gnu
cfg: enabling more debugging (CFG_ENABLE_DEBUG)
cfg: host for i686-unknown-linux-gnu is i386
cfg: host for x86_64-unknown-linux-gnu is x86_64
cfg: os for i686-unknown-linux-gnu is unknown-linux-gnu
cfg: os for x86_64-unknown-linux-gnu is unknown-linux-gnu
cfg: using ccache gcc
cfg: enabling valgrind (CFG_ENABLE_VALGRIND)
cfg: no pdflatex found, deferring to xelatex
cfg: no xelatex found, deferring to lualatex
cfg: no lualatex found, disabling LaTeX docs
cfg: no pandoc found, omitting PDF and EPUB docs
cfg: no llnextgen found, omitting grammar-verification
MATCHES=""; if [ -n "$MATCHES" ] ; then echo "warning: removing previous" \'liblibc-*.so\' "libraries:" $MATCHES; rm $MATCHES ; fi
MATCHES=""; if [ -n "$MATCHES" ] ; then echo "warning: removing previous" \'liblibc-*.rlib\' "libraries:" $MATCHES; rm $MATCHES ; fi
LD_LIBRARY_PATH="$LD_LIBRARY_PATH:/home/alex/code/rust4/x86_64-unknown-linux-gnu/stage1/lib"   x86_64-unknown-linux-gnu/stage1/bin/rustc --cfg stage1  -O --cfg rtopt --cfg debug -C prefer-dynamic --target=i686-unknown-linux-gnu -C linker=ccache g++ -C ar=ar   -D warnings -L "i686-unknown-linux-gnu/rt" -L "/home/alex/code/rust4/i686-unknown-linux-gnu/llvm/Release+Asserts/lib" -L "/usr/lib/gcc/x86_64-linux-gnu/4.8/" --out-dir x86_64-unknown-linux-gnu/stage1/lib/rustlib/i686-unknown-linux-gnu/lib /home/alex/code/rust4/src/liblibc/lib.rs
error: multiple input filenames provided

The reason for this is that the command line has -C linker=ccache g++ and rustc then interprets g++ as an input file. Note that quoting also doesn't solve the problem because "ccache g++" is not a binary on the system.