Some binaries are built in error

[Lokathor]

Per the discussion in #34, some binaries are being built and left around despite them not even being used by the library.

d:\dev\learn-gfx-hal\target\debug\build\shaderc-0b3a14f59f26d605\out\bin>dir
 Volume in drive D is Data
 Volume Serial Number is B265-51AB

 Directory of d:\dev\learn-gfx-hal\target\debug\build\shaderc-0b3a14f59f26d605\out\bin

2019-01-25  09:07 PM    <DIR>          .
2019-01-25  09:07 PM    <DIR>          ..
2019-01-25  09:06 PM         3,981,312 glslangValidator.exe
2019-01-25  09:06 PM         4,111,360 glslc.exe
2019-01-25  09:07 PM         4,038,144 shaderc_shared.dll
2019-01-15  09:01 AM               866 spirv-lesspipe.sh
2019-01-25  09:07 PM           218,624 spirv-remap.exe
2019-01-25  09:06 PM         1,156,608 SPIRV-Tools-shared.dll