Compiling with "gmake" should produce less output. The compilation/linking

Compiling with "gmake" should produce less output. The compilation/linking
flags are always the same anyway, who wants to see so much text on the
screen? Compiling with "gmake VERBOSE=1" should produce all the output
you're used to.

Basically it checks for VERBOSE being defined, and if it is, sets VERB
appropriately. VERB is then prepended in a bunch of key places such that
when VERB is "@", the command is not echoed, when VERB is not set to
anything, it's as before.

One thing I could not get rid of is "gmake[1]: Entering directory <blah>",
but running "gmake -s" suppresses it all, and shows just the interesting
stuff.

Now output (when running "gmake -s" will look something like):

<snip>
======= Linking target debug library =======
Compiling Writer.cpp
Compiling getLLVMinfo.cpp
Compiling as.cpp
Compiling dis.cpp
Compiling opt.cpp
Compiling gccas.cpp
<snip>

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@3686 91177308-0d34-0410-b5e6-96231b3b80d8