Fix warnings from clang 3.2
Minimize non-error cmake output, unless VERBOSE=1
Minor improvement to recent exit() fix -- if the shader has no exit() call,
do not generate the extra branch & basic block.

This turns out to be important -- if we put the branch in there
unconditionally, and everything else is optimized away, it no longer looks
like the post-optimized IR is "empty", so the shader isn't flagged as
empty.  When displacement shaders are empty, our renderer handles the
dicing differently.  Hilarity ensues.
Windows port: add OSL_STATIC_LIBRARY define to disable dllimport/dllexport
when using BUILDSTATIC. The application linking against OSL needs to define
this if wants to link against a static OSL library on Windows.

Also fix build errors adding dllimport/dllexport on class members when the
class had them already.
Rename strtoi/strtof -> stoi/stof to match C++11 nomenclature
Windows port: Fix crash using fmod() on Windows 32 bit. This generates an
instruction which doesn't seem to be supported, probably need compiler-rt
for this but I couldn't get it working, so now it's compiled as a function.

Relevant LLVM bug reports:
http://llvm.org/bugs/show_bug.cgi?id=5053
http://llvm.org/bugs/show_bug.cgi?id=5052
Add support for newer gcc version in Imageworks builds
Switch to LLVM 3.2 in Imageworks builds
Windows port: fix mysterious threading crash in creating llvm module and memory
manager. The cause of this is unclear, a mutex lock works around it.