use "no-underscore" naming convention for 64-bit Windows

GCC 4.5.1 and later use a naming convention where functions are not
prefixed with an underscore, whereas previous versions added the
underscore.  This change was made to ensure compatibility with
Microsoft's compiler.  Since GCC 4.5.0 has a serious code generation
bug, we now only support later versions, so it makes sense to assume
the newer convention.

readme.txt

@@ -62,7 +62,7 @@ Building
 Build requirements include:
 
   * GNU make 3.80 or later
-  * GCC 3.4 or later (4.5 or later for Windows/x86_64)
+  * GCC 3.4 or later (4.5.1 or later for Windows/x86_64)
   * JDK 1.5 or later
   * MinGW 3.4 or later (only if compiling for Windows)
   * zlib 1.2.3 or later

src/boot.cpp

@@ -32,7 +32,7 @@ extern "C" void __cxa_pure_virtual(void) { abort(); }
 
 #ifdef BOOT_IMAGE
 
-#if (defined __MINGW32__) || (defined _MSC_VER)
+#if (! defined __x86_64__) && ((defined __MINGW32__) || (defined _MSC_VER))
 #  define SYMBOL(x) binary_bootimage_bin_##x
 #else
 #  define SYMBOL(x) _binary_bootimage_bin_##x
@@ -58,7 +58,7 @@ extern "C" {
 
 #ifdef BOOT_CLASSPATH
 
-#if (defined __MINGW32__) || (defined _MSC_VER)
+#if (! defined __x86_64__) && ((defined __MINGW32__) || (defined _MSC_VER))
 #  define SYMBOL(x) binary_classpath_jar_##x
 #else
 #  define SYMBOL(x) _binary_classpath_jar_##x

src/compile-x86.S

@@ -12,7 +12,8 @@
 
 #define LOCAL(x) .L##x
 
-#if defined __APPLE__ || defined __MINGW32__ || defined __CYGWIN32__
+#if defined __APPLE__ \
+   || ((defined __MINGW32__ || defined __CYGWIN32__) && ! defined __x86_64__)
 #  define GLOBAL(x) _##x
 #else
 #  define GLOBAL(x) x   

src/x86.S

@@ -12,7 +12,8 @@
 
 #define LOCAL(x) .L##x
 
-#if defined __APPLE__ || defined __MINGW32__ || defined __CYGWIN32__
+#if defined __APPLE__ \
+   || ((defined __MINGW32__ || defined __CYGWIN32__) && ! defined __x86_64__)
 #  define GLOBAL(x) _##x
 #else
 #  define GLOBAL(x) x