Avoid leading dot slash in cmake target. (google#570)

Including shaderc in project that declares multiple build configurations
and then using generator that doesn't support multi-configuration would
result in a target path with a leading dot slash.  Ninja doesn't work
in that case.

Prepend CMAKE_CURRENT_BINARY_DIR in order to get an absolute path and
make ninja happy.  This works in all cases so we remove code specific
to multi-configuration.

Fixes google#568.

cmake/utils.cmake

@@ -161,15 +161,7 @@ function(shaderc_combine_static_lib new_target target)
  shaderc_get_transitive_libs(${target} all_libs)
 
  set(libname
- ${CMAKE_CURRENT_BINARY_DIR}/${CMAKE_STATIC_LIBRARY_PREFIX}${new_target}${CMAKE_STATIC_LIBRARY_SUFFIX})
-
- if (CMAKE_CONFIGURATION_TYPES)
- list(LENGTH CMAKE_CONFIGURATION_TYPES num_configurations)
- if (${num_configurations} GREATER 1)
- set(libname
- ${CMAKE_CFG_INTDIR}/${CMAKE_STATIC_LIBRARY_PREFIX}${new_target}${CMAKE_STATIC_LIBRARY_SUFFIX})
- endif()
- endif()
+ ${CMAKE_CURRENT_BINARY_DIR}/${CMAKE_CFG_INTDIR}/${CMAKE_STATIC_LIBRARY_PREFIX}${new_target}${CMAKE_STATIC_LIBRARY_SUFFIX})
 
  if (MSVC)
  string(REPLACE ";" ">;$<TARGET_FILE:" temp_string "${all_libs}")