win32: add minimal mingw header shellapi.h

This is a very stripped down version[1], with only CommandLineToArgvW
(typically used with GetCommandLineW() - which we already have),
ShellExecute and FindExecutable, which don't require any new structs,
and where used constants already exist at our winuser.h .

Pretty cheap, and hopefully covers some meaningful new use cases[2].

Requires linking with -lshell32 .

[1] original full version:
http://download.savannah.nongnu.org/releases/tinycc/winapi-full-for-0.9.27.zip

[2] Can now build "less" for windows - https://github.com/gwsw/less/ .
Add -luser32 to LIBS at Makefile.wng (mingw makefile), then (gnu make):
  make -f Makefile.wng CC=tcc less.exe

win32/include/winapi/shellapi.h

@@ -0,0 +1,59 @@
+/**
+ * This file has no copyright assigned and is placed in the Public Domain.
+ * This file is part of the w64 mingw-runtime package.
+ * No warranty is given; refer to the file DISCLAIMER within this package.
+ */
+#ifndef _INC_SHELLAPI
+#define _INC_SHELLAPI
+
+#ifndef WINSHELLAPI
+#if !defined(_SHELL32_)
+#define WINSHELLAPI DECLSPEC_IMPORT
+#else
+#define WINSHELLAPI
+#endif
+#endif
+
+#ifndef SHSTDAPI
+#if !defined(_SHELL32_)
+#define SHSTDAPI EXTERN_C DECLSPEC_IMPORT HRESULT WINAPI
+#define SHSTDAPI_(type) EXTERN_C DECLSPEC_IMPORT type WINAPI
+#else
+#define SHSTDAPI STDAPI
+#define SHSTDAPI_(type) STDAPI_(type)
+#endif
+#endif
+
+/* SHDOCAPI[_] definitions not required in this TinyCC minimal header */
+
+#if !defined(_WIN64)
+#include <pshpack1.h>
+#endif
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#ifdef UNICODE
+#define ShellExecute ShellExecuteW
+#define FindExecutable FindExecutableW
+#else
+#define ShellExecute ShellExecuteA
+#define FindExecutable FindExecutableA
+#endif
+
+  /* minimal subset distributed with TinyCC. nShowCmd is at winuser.h */
+  SHSTDAPI_(HINSTANCE) ShellExecuteA(HWND hwnd,LPCSTR lpOperation,LPCSTR lpFile,LPCSTR lpParameters,LPCSTR lpDirectory,INT nShowCmd);
+  SHSTDAPI_(HINSTANCE) ShellExecuteW(HWND hwnd,LPCWSTR lpOperation,LPCWSTR lpFile,LPCWSTR lpParameters,LPCWSTR lpDirectory,INT nShowCmd);
+  SHSTDAPI_(HINSTANCE) FindExecutableA(LPCSTR lpFile,LPCSTR lpDirectory,LPSTR lpResult);
+  SHSTDAPI_(HINSTANCE) FindExecutableW(LPCWSTR lpFile,LPCWSTR lpDirectory,LPWSTR lpResult);
+  SHSTDAPI_(LPWSTR *) CommandLineToArgvW(LPCWSTR lpCmdLine,int*pNumArgs);
+
+#ifdef __cplusplus
+}
+#endif
+
+#if !defined(_WIN64)
+#include <poppack.h>
+#endif
+#endif