Provide <triplet>-<tool> wrappers and links to many llvm tools

Provide wrappers named <triplet>-gcc and <triplet>-g++ as well,
to ease cross compilation with e.g. autotools, to allow just
specifying --host=<triplet>.

Provide wrappers for objdump and ld that provide specific output
that autotools look for.

Provide <triplet>-strip as a symlink to /bin/true, since there is
no strip tool available yet (and llvm-objcopy doesn't support
COFF yet).

Dockerfile

@@ -21,7 +21,7 @@ RUN ./build-llvm.sh $TOOLCHAIN_PREFIX
 ENV TOOLCHAIN_ARCHS="i686 x86_64 armv7 aarch64"
 
 # Install the usual $TUPLE-clang binaries
-COPY wrappers/clang-target-wrapper.sh ./wrappers/
+COPY wrappers/*.sh ./wrappers/
 COPY install-wrappers.sh .
 RUN ./install-wrappers.sh $TOOLCHAIN_PREFIX