cmake: check for math library functions even in the absence of libm

(Reference issue: https://github.com/libsdl-org/SDL/issues/7011)

CMakeLists.txt

@@ -1047,7 +1047,8 @@ if(SDL_LIBC)
     check_library_exists(m pow "" HAVE_LIBM)
     if(HAVE_LIBM)
       set(CMAKE_REQUIRED_LIBRARIES m)
-      foreach(_FN
+    endif()
+    foreach(_FN
               atan atan2 atanf atan2f ceil ceilf copysign copysignf cos cosf
               exp expf fabs fabsf floor floorf fmod fmodf log logf log10 log10f
               lround lroundf pow powf round roundf scalbn scalbnf sin sinf sqrt
@@ -1055,7 +1056,8 @@ if(SDL_LIBC)
         string(TOUPPER ${_FN} _UPPER)
         set(_HAVEVAR "HAVE_${_UPPER}")
         check_symbol_exists("${_FN}" "math.h" ${_HAVEVAR})
-      endforeach()
+    endforeach()
+    if(HAVE_LIBM)
       set(CMAKE_REQUIRED_LIBRARIES)
       if(NOT VITA)
         list(APPEND EXTRA_LIBS m)