Adds support for pcg32 library (#1195)

* Adds support for pcg32 library

* Adds fake version for pcg32; simplifies head-only

packages/p/pcg32/xmake.lua

@@ -0,0 +1,19 @@
+package("pcg32")
+    set_homepage("https://github.com/wjakob/pcg32")
+    set_description("Tiny self-contained C++ version of the PCG32 pseudorandom number generator")
+    set_license("Apache-2.0")
+
+    add_urls("https://github.com/wjakob/pcg32.git")
+
+    -- A fake version since no any releases/tags
+    add_versions("2016.06.07", "70099eadb86d3999c38cf69d2c55f8adc1f7fe34")
+
+    on_install("windows", "linux", "macosx", function (package)
+        os.cp("pcg32.h", package:installdir("include/pcg32"))
+    end)
+
+    on_test(function (package)
+        assert(package:check_cxxsnippets({test = [[
+            pcg32 rng;
+        ]]}, {configs = {languages = "cxx17"}, includes = "pcg32/pcg32.h"}))
+    end)