MinGW64 requires that the functions be prefixed with an underscore. Visual C++ apparently doesn't

simd/jsimdext.inc

@@ -47,7 +47,9 @@
 ;
 %define SEG_TEXT    .text  align=16 public use64 class=CODE
 %define SEG_CONST   .rdata align=16 public use64 class=CONST
-;%define EXTN(name)  name			; foo() -> foo
+%ifdef MSVC
+%define EXTN(name)  name			; foo() -> foo
+%endif
 
 %elifdef OBJ32	; ----(nasm -fobj -DOBJ32 ...)----------
 ; * Borland C++ (Win32)

win/Makerules

@@ -30,9 +30,9 @@ endif
 CFLAGS = -W3 -wd4996 -Iwin -I.
 CDEFINES = -DWIN32 -D_CRT_SECURE_NO_DEPRECATE
 ifeq ($(WIN64), yes)
-NAFLAGS = -fwin64 -DWIN64 -D__x86_64__ -Iwin/
+NAFLAGS = -fwin64 -DWIN64 -DMSVC -D__x86_64__ -Iwin/
 else
-NAFLAGS = -fwin32 -DWIN32 -Iwin/
+NAFLAGS = -fwin32 -DWIN32 -DMSVC -Iwin/
 endif
 ifeq ($(DEBUG), yes)
  CFLAGS := $(CFLAGS) -Od -MTd -Zi