https://github.com/FFTW/fftw3/pull/232
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -134,6 +134,7 @@ include (CheckCCompilerFlag)
 if (ENABLE_SSE)
   foreach (FLAG "-msse" "/arch:SSE")
     unset (HAVE_SSE CACHE)
+	unset (HAVE_SSE)
     check_c_compiler_flag (${FLAG} HAVE_SSE)
     if (HAVE_SSE)
       set (SSE_FLAG ${FLAG})
@@ -145,6 +146,7 @@ endif ()
 if (ENABLE_SSE2)
   foreach (FLAG "-msse2" "/arch:SSE2")
     unset (HAVE_SSE2 CACHE)
+	unset (HAVE_SSE2)
     check_c_compiler_flag (${FLAG} HAVE_SSE2)
     if (HAVE_SSE2)
       set (SSE2_FLAG ${FLAG})
@@ -156,6 +158,7 @@ endif ()
 if (ENABLE_AVX)
   foreach (FLAG "-mavx" "/arch:AVX")
     unset (HAVE_AVX CACHE)
+	unset (HAVE_AVX)
     check_c_compiler_flag (${FLAG} HAVE_AVX)
     if (HAVE_AVX)
       set (AVX_FLAG ${FLAG})
@@ -167,6 +170,7 @@ endif ()
 if (ENABLE_AVX2)
   foreach (FLAG "-mavx2" "/arch:AVX2")
     unset (HAVE_AVX2 CACHE)
+	unset (HAVE_AVX2)
     check_c_compiler_flag (${FLAG} HAVE_AVX2)
     if (HAVE_AVX2)
       set (AVX2_FLAG ${FLAG})
@@ -179,6 +183,7 @@ endif ()
 if (ENABLE_AVX2)
   foreach (FLAG "-mfma" "/arch:FMA")
     unset (HAVE_FMA CACHE)
+	unset (HAVE_FMA)
     check_c_compiler_flag (${FLAG} HAVE_FMA)
     if (HAVE_FMA)
       set (FMA_FLAG ${FLAG})