Add zig buildfile for examples. (#2051)

* Add zig buildfile for examples.

- `zig build` to compile all examples
- `zig build [module]` to compile all examples for a module (e.g. `zig build core`)
- `zig build [example]` to compile _and run_ a particular example (e.g. `zig build core_basic_window`)

You can use `-Dtarget=` to compile for a non-native platform, such as
`zig build -Dtarget=x86_64-windows-gnu` to compile from Linux to
Windows.

* Skip pthread example on Windows.

* Select appropriate lib file based on target.

examples/README.md

@@ -1,3 +1,21 @@
+## Building the Examples
+
+The examples assume you have already built the `raylib` library in `../src`.
+
+### With GNU make
+
+- `make` builds all examples
+- `make [module]` builds all examples for a particular module (e.g `make core`)
+
+### With Zig
+
+The [Zig](https://ziglang.org/) toolchain can compile `C` and `C++` in addition to `Zig`.
+You may find it easier to use than other toolchains, especially when it comes to cross-compiling.
+
+- `zig build` to compile all examples
+- `zig build [module]` to compile all examples for a module (e.g. `zig build core`)
+- `zig build [example]` to compile _and run_ a particular example (e.g. `zig build core_basic_window`)
+
 ## EXAMPLES LIST
 
 ### category: core