add support for 32-bit ARM on Windows (#477)

* add support for 32-bit ARM on Windows

* fix mismatched brace in appveyor.yml

* remove arm platform from appveyor.yml for now

* fix arm build

* fix typo

* fix assembler names

* try Visual Studio 2017

* add windows arm32 to .appveyor.yml

* update README.md

src/arm/ffitarget.h

@@ -43,7 +43,7 @@ typedef enum ffi_abi {
   FFI_SYSV,
   FFI_VFP,
   FFI_LAST_ABI,
-#ifdef __ARM_PCS_VFP
+#if defined(__ARM_PCS_VFP) || defined(_M_ARM)
   FFI_DEFAULT_ABI = FFI_VFP,
 #else
   FFI_DEFAULT_ABI = FFI_SYSV,
@@ -57,7 +57,9 @@ typedef enum ffi_abi {
   signed char vfp_args[16]			\
 
 #define FFI_TARGET_SPECIFIC_VARIADIC
+#ifndef _M_ARM
 #define FFI_TARGET_HAS_COMPLEX_TYPE
+#endif
 
 /* ---- Definitions for closures ----------------------------------------- */
 
@@ -74,8 +76,13 @@ typedef enum ffi_abi {
 #error "No trampoline table implementation"
 #endif
 
+#else
+#ifdef _MSC_VER
+#define FFI_TRAMPOLINE_SIZE 16
+#define FFI_TRAMPOLINE_CLOSURE_FUNCTION 12
 #else
 #define FFI_TRAMPOLINE_SIZE 12
+#endif
 #define FFI_TRAMPOLINE_CLOSURE_OFFSET FFI_TRAMPOLINE_SIZE
 #endif