Minor CMake improvements

* Update minimum version to 3.1 for CMP0054 new behaviour
* Use stricter PRECISION regex matching
* Use imported target Threads::Threads instead of CMAKE_THREAD_LIBS_INIT

Author: lukas-w

CMakeLists.txt

@@ -1,4 +1,4 @@
-cmake_minimum_required (VERSION 3.0)
+cmake_minimum_required (VERSION 3.1)
 
 if (NOT DEFINED CMAKE_BUILD_TYPE)
   set (CMAKE_BUILD_TYPE Release CACHE STRING "Build type")
@@ -269,7 +269,7 @@ if (BUILD_SHARED_LIBS)
 endif ()
 
 function (add_fftw_library PRECISION)
-  if (PRECISION MATCHES "SINGLE|LDOUBLE|QUAD")
+  if (PRECISION MATCHES "^(SINGLE|LDOUBLE|QUAD)$")
     set (FFTW_${PRECISION} TRUE)
     set (BENCHFFT_${PRECISION} TRUE)
     if (PRECISION STREQUAL SINGLE)
@@ -313,11 +313,11 @@ function (add_fftw_library PRECISION)
 
   if (ENABLE_THREADS AND Threads_FOUND)
     if (WITH_COMBINED_THREADS)
-      target_link_libraries (${fftw3_lib} ${CMAKE_THREAD_LIBS_INIT})
+      target_link_libraries (${fftw3_lib} Threads::Threads)
     else ()
       add_library (${fftw3_lib}_threads ${fftw_threads_SOURCE})
       target_link_libraries (${fftw3_lib}_threads ${fftw3_lib})
-      target_link_libraries (${fftw3_lib}_threads ${CMAKE_THREAD_LIBS_INIT})
+      target_link_libraries (${fftw3_lib}_threads Threads::Threads)
       list (APPEND subtargets ${fftw3_lib}_threads)
     endif ()
   endif ()