[mypyc] lib-rt base64: support pyodide for Python 3.12

For Python 3.12, pyodide requires emscripten 3.1.{46,52,58}, which uses an older
version of SIMDe that doesn't include all the NEON 64-bit intrinsics we need.

So we use the 32-bit NEON intrinsics implementation of base64 for Pyodide on
Python 3.12, and use the 64-bit NEON intrinsics implementations of
base64 for Pyodide on Python 3.13.

Pyodide for Python 3.13 uses emscripten 4.0.{6,8,9}

Emscripten versdion 3.1.63 appears to be the first version with the
updated SIMDe versions:

emscripten-core/emscripten@6223c43

Author: mr-c

mypyc/lib-rt/base64/config.h

@@ -8,17 +8,15 @@
   #define HAVE_AVX 1
   #define HAVE_AVX2 1
   #define HAVE_AVX512 0
+#elif (defined(__APPLE__) && defined(__aarch64__))
+  #define HAVE_NEON64 1
+#elif (defined(__wasm__) && defined(__wasm_simd128__))
+  #include "emscripten/version.h"
+  #if __EMSCRIPTEN_major__ == 3
+    #define HAVE_NEON32 1
+  #elif __EMSCRIPTEN_major__ > 3
+    #define HAVE_NEON64 1
+  #endif
 #endif
 
-#define BASE64_WITH_NEON32 0
-#define HAVE_NEON32 BASE64_WITH_NEON32
-
-#if (defined(__APPLE__) && defined(__aarch64__)) || (defined(__wasm__) && defined(__wasm_simd128__))
-#define BASE64_WITH_NEON64 1
-#else
-#define BASE64_WITH_NEON64 0
-#endif
-
-#define HAVE_NEON64 BASE64_WITH_NEON64
-
 #endif // BASE64_CONFIG_H