CMake: Detect libm with find_library (#596)

CMakeLists.txt

@@ -80,8 +80,6 @@ include (CheckTypeSize)
 include (CheckCCompilerFlag)
 include (CheckCXXSymbolExists)
 include (CheckCSourceCompiles)
-include (CheckCXXCompilerFlag)
-include (CheckLibraryExists)
 
 #==============================================================================
 # COMPILATION CHECKINGS and CONFIGURATION GENERATION
@@ -108,9 +106,8 @@ set (HAVE_UINT32_T ${SIZEOF_UINT32_T})
 check_type_size ("unsigned int" SIZEOF_UNSIGNED_INT)
 check_type_size ("unsigned long" SIZEOF_UNSIGNED_LONG)
 
-check_library_exists ("m" sqrt "" HAVE_LIBM)
-if (HAVE_LIBM)
-  set (M_LIBRARY m)
+find_library(M_LIBRARY m)
+if (M_LIBRARY)
   set (LIBS_PRIVATE "-l${M_LIBRARY}")
 endif()
 
@@ -258,7 +255,9 @@ if (NLOPT_LUKSAN)
   target_include_directories(${nlopt_lib} PRIVATE src/algs/luksan)
   target_compile_definitions (${nlopt_lib} PRIVATE NLOPT_LUKSAN)
 endif ()
-target_link_libraries (${nlopt_lib} ${M_LIBRARY})
+if (M_LIBRARY)
+  target_link_libraries (${nlopt_lib} ${M_LIBRARY})
+endif ()
 set_target_properties (${nlopt_lib} PROPERTIES SOVERSION ${SO_MAJOR})
 set_target_properties (${nlopt_lib} PROPERTIES VERSION "${SO_MAJOR}.${SO_MINOR}.${SO_PATCH}")