mssql: support windows (#10336)

thirdparty/mssql/include/.gitignore

@@ -0,0 +1,4 @@
+*
+
+!.gitignore
+!mssql.h

thirdparty/mssql/include/mssql.h

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+// Hacking some headers in windows.
+// sql headers using UNICODE to change function signatures.
+// Currently Linux bindings do not use unicode SQL C bindings,
+// So we turn off the UNICODE to make it compile on windows.
+// For future Unicode support, please raise a issue.
+
+#include <windows.h>
+#include <sal.h>
+
+#ifdef UNICODE
+// Turn off unicode macro and turn back on, so it only affects sql headers
+#undef UNICODE
+#include <sql.h>
+#include <sqlext.h>
+#define UNICODE
+
+#else
+#include <sql.h>
+#include <sqlext.h>
+#endif

vlib/mssql/README.md

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 ## Dependencies
 * ODBC C/C++ library
-    * Linux Install: https://docs.microsoft.com/en-us/sql/connect/odbc/linux-mac/installing-the-microsoft-odbc-driver-for-sql-server
+    * Linux Install: 
-        * `msodbcsql17` and `unixodbc-dev` packages needed
+		* Details: https://docs.microsoft.com/en-us/sql/connect/odbc/linux-mac/installing-the-microsoft-odbc-driver-for-sql-server
-    * Windows Install: https://docs.microsoft.com/en-us/sql/connect/odbc/microsoft-odbc-driver-for-sql-server
+        * `msodbcsql17` and `unixodbc-dev` packages are needed
+    * Windows Install:
+		* `odbc` lib is included in windows sdk for most of distributions,
+			so there is no need to install it separately
+		* Details: https://docs.microsoft.com/en-us/sql/connect/odbc/microsoft-odbc-driver-for-sql-server
+
+## Windows Notes
+### Using `msvc`
+* Make sure `cl.exe` of `msvc` is accessible from command line. 
+You can run `v` commands in `Visual Studio 2019 Developer Command Prompt` to be safe.
+* C Headers and dlls can be automatically resolved by `msvc`.
+### Using `tcc` 
+* Copy those headers to `@VEXEROOT\thirdparty\mssql\include`. 
+The version number `10.0.18362.0` might differ on your system. 
+Command Prompt commands:
+```cmd
+copy "C:\Program Files (x86)\Windows Kits\10\Include\10.0.18362.0\um\sql.h" thirdparty\mssql\include
+copy "C:\Program Files (x86)\Windows Kits\10\Include\10.0.18362.0\um\sqlext.h" thirdparty\mssql\include
+copy "C:\Program Files (x86)\Windows Kits\10\Include\10.0.18362.0\um\sqltypes.h" thirdparty\mssql\include
+copy "C:\Program Files (x86)\Windows Kits\10\Include\10.0.18362.0\um\sqlucode.h" thirdparty\mssql\include
+copy "C:\Program Files (x86)\Windows Kits\10\Include\10.0.18362.0\shared\sal.h" thirdparty\mssql\include
+copy "C:\Program Files (x86)\Windows Kits\10\Include\10.0.18362.0\shared\concurrencysal.h" thirdparty\mssql\include
+```
+* dlls can be automatically resolved by `tcc`
 
 ## TODO
-* Support Windows
 * Support Mac 
-* ORM
+* Support ORM
 
 ## Usage
 ```v ignore

vlib/mssql/_cdef_windows.c.v

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 module mssql
 
-// TODO: implement windows
+// mssql module does not support tcc on windows
-// #flag windows -I@VEXEROOT/thirdparty/msodbcsql17
+
-// #flag windows @VEXEROOT/thirdparty/msodbcsql17/lib64
+// odbc32 lib comes with windows sdk and does not need to be installed separately.
+// v builder for msvc can resolve the sdk includes search path, so no need to repeat here.
+#flag windows -lodbc32
+
+// Special handling of sql headers on windows.
+// Source is in v third party folder.
+#flag windows -I@VEXEROOT/thirdparty/mssql/include
+#include <mssql.h>