Fix pkgconfig 'Version' w/ USE=examples
https://bugs.gentoo.org/657300

--- a/CMakeLists.txt	2018-02-23 23:39:25.000000000 +0200
+++ b/CMakeLists.txt	2018-06-03 22:26:38.673844365 +0300
@@ -3,7 +3,7 @@
 
 cmake_minimum_required (VERSION 3.1 FATAL_ERROR)
 
-project (soxr C)
+project (soxr)
 set (DESCRIPTION_SUMMARY
     "High quality, one-dimensional sample-rate conversion library")
 
@@ -100,10 +100,6 @@
   set (LIBM_LIBRARIES m)
 endif ()
 
-if (${BUILD_EXAMPLES})
-  project (${PROJECT_NAME}) # Adds c++ compiler
-endif ()
-
 if (WITH_OPENMP)
   find_package (OpenMP)
   if (OPENMP_FOUND)