port: record initial MSVC600 compatibility layer

PORT_STATUS.md

@@ -40,10 +40,12 @@ The next errors include:
 - additional C99/C99-era declarations and compatibility assumptions
 
 The compatibility header now supplies the pointer-sized typedefs required by
-`pyport.h`; the current first compiler diagnostics are unsupported C `inline`
+`pyport.h`; the current first compiler diagnostics after applying the saved
-syntax and `__declspec(deprecated)` annotations in CPython headers. The shim
+`compat/msvc600/cpython-3.11.16-vc6-headers.patch` are VC6's inability to parse
-resolved only the missing-header and pointer-type layer; it is intentionally not
+`long long` declarations in `Include/longobject.h` and C99-style integer
-presented as a complete fix.
+literal suffixes in `Include/pythread.h`. The shim and patch resolve only the
+missing-header, pointer-type, inline, and deprecation layers; they are
+intentionally not presented as a complete fix.
 
 ## Larger blockers to plan for
 

compat/msvc600/cpython-3.11.16-vc6-headers.patch

@@ -0,0 +1,34 @@
+diff --git a/Include/pyport.h b/Include/pyport.h
+index b3b8b6f..4da45ef 100644
+--- a/Include/pyport.h
++++ b/Include/pyport.h
+@@ -334,9 +334,12 @@ extern "C" {
+ #if defined(__GNUC__) \
+     && ((__GNUC__ >= 4) || (__GNUC__ == 3) && (__GNUC_MINOR__ >= 1))
+ #define Py_DEPRECATED(VERSION_UNUSED) __attribute__((__deprecated__))
+-#elif defined(_MSC_VER)
++#elif defined(_MSC_VER) && _MSC_VER >= 1300
+ #define Py_DEPRECATED(VERSION) __declspec(deprecated( \
+                                           "deprecated in " #VERSION))
++#elif defined(_MSC_VER)
++/* Visual C++ 6.0 has no supported deprecation declaration syntax. */
++#define Py_DEPRECATED(VERSION_UNUSED)
+ #else
+ #define Py_DEPRECATED(VERSION_UNUSED)
+ #endif
+@@ -352,10 +355,14 @@ extern "C" {
+ #define _Py_COMP_DIAG_IGNORE_DEPR_DECLS \
+     _Pragma("GCC diagnostic ignored \"-Wdeprecated-declarations\"")
+ #define _Py_COMP_DIAG_POP _Pragma("GCC diagnostic pop")
+-#elif defined(_MSC_VER)
++#elif defined(_MSC_VER) && _MSC_VER >= 1300
+ #define _Py_COMP_DIAG_PUSH __pragma(warning(push))
+ #define _Py_COMP_DIAG_IGNORE_DEPR_DECLS __pragma(warning(disable: 4996))
+ #define _Py_COMP_DIAG_POP __pragma(warning(pop))
++#elif defined(_MSC_VER)
++#define _Py_COMP_DIAG_PUSH
++#define _Py_COMP_DIAG_IGNORE_DEPR_DECLS
++#define _Py_COMP_DIAG_POP
+ #else
+ #define _Py_COMP_DIAG_PUSH
+ #define _Py_COMP_DIAG_IGNORE_DEPR_DECLS

compat/msvc600/inttypes.h

@@ -31,4 +31,9 @@ typedef unsigned __int64 uint_least64_t;
 #define PRIx64 "I64x"
 #define PRIX64 "I64X"
 
+/* VC6 has __inline but does not recognize the C99 inline keyword. */
+#ifndef inline
+#define inline __inline
+#endif
+
 #endif