add exprtk and strtk (#786 An error occurred )

* add exprtk

* add strtk

packages/e/exprtk/xmake.lua

@@ -0,0 +1,36 @@
+package("exprtk")
+
+    set_kind("library", {headeronly = true})
+    set_homepage("https://www.partow.net/programming/exprtk/index.html")
+    set_description("C++ Mathematical Expression Parsing And Evaluation Library")
+    set_license("MIT")
+
+    add_urls("https://github.com/ArashPartow/exprtk.git")
+    add_versions("2021.06.06", "93a9f44f99b910bfe07cd1e933371e83cea3841c")
+
+    if is_plat("windows") then
+        add_cxxflags("/bigobj")
+    elseif is_plat("mingw") then
+        add_cxxflags("-Wa,-mbig-obj")
+    end
+    on_install(function (package)
+        os.cp("exprtk.hpp", package:installdir("include"))
+    end)
+
+    on_test(function (package)
+        assert(package:check_cxxsnippets({test = [[
+            void test() {
+                double x;
+                const std::string expression_string =
+                    "clamp(-1.0,sin(2 * pi * x) + cos(x / 2 * pi),+1.0)";
+                exprtk::symbol_table<double> symbol_table;
+                exprtk::expression<double> expression;
+                exprtk::parser<double> parser;
+
+                symbol_table.add_variable("x",x);
+                symbol_table.add_constants();
+                expression.register_symbol_table(symbol_table);
+                parser.compile(expression_string,expression);
+            }
+        ]]}, {configs = {languages = "c++14"}, includes = "exprtk.hpp"}))
+    end)

packages/s/strtk/xmake.lua

@@ -0,0 +1,26 @@
+package("strtk")
+
+    set_kind("library", {headeronly = true})
+    set_homepage("https://www.partow.net/programming/strtk/index.html")
+    set_description("C++ String Toolkit Library")
+    set_license("MIT")
+
+    add_urls("https://github.com/ArashPartow/strtk.git")
+    add_versions("2020.01.01", "d2b446bf1f7854e8b08f5295ec6f6852cae066a2")
+
+    on_install(function (package)
+        os.cp("strtk.hpp", package:installdir("include"))
+    end)
+
+    on_test(function (package)
+        assert(package:check_cxxsnippets({test = [[
+            #define strtk_no_tr1_or_boost
+            #include <strtk.hpp>
+            void test() {
+                std::string s = "abc|123|xyz|789";
+                strtk::single_delimiter_predicate<std::string::value_type> predicate('|');
+                strtk::std_string::tokenizer<>::type tokenizer(s,predicate);
+                strtk::std_string::tokenizer<>::type::iterator itr = tokenizer.begin();
+            }
+        ]]}, {configs = {languages = "c++14"}}))
+    end)