Try to fix build on MinGW32

Author: pitrou

cpp/src/arrow/vendored/fast_float/float_common.h

@@ -8,7 +8,8 @@
 #include <strings.h>
 #endif
 
-#if defined(_MSC_VER) && !defined(__clang__)
+#if defined(_WIN32) && !defined(__clang__)
+// Note this also covers MinGW
 #define FASTFLOAT_VISUAL_STUDIO 1
 #endif
 
@@ -18,7 +19,7 @@
 #define fastfloat_really_inline inline __attribute__((always_inline))
 #endif 
 
-#ifdef _MSC_VER
+#ifdef _WIN32
 #define fastfloat_strcasecmp _stricmp
 #define fastfloat_strncasecmp _strnicmp
 #else
@@ -106,7 +107,7 @@ fastfloat_really_inline value128 full_multiplication(uint64_t value1, uint64_t v
   return answer;
 }
 
-#else
+#else  // !FASTFLOAT_VISUAL_STUDIO
 
 // compute value1 * value2
 fastfloat_really_inline