add libgit2 (#686)

* add libgit2

* Update xmake.lua

* Update xmake.lua

* Update xmake.lua

* improve libgit2

* improve libgit2

* update libgit2 for windows

* add syslinks for windows

packages/l/libgit2/xmake.lua

@@ -0,0 +1,48 @@
+package("libgit2")
+
+    set_homepage("https://libgit2.org/")
+    set_description("A cross-platform, linkable library implementation of Git that you can use in your application.")
+    set_license("GPL-2.0-only")
+
+    set_urls("https://github.com/libgit2/libgit2/archive/refs/tags/$(version).tar.gz",
+             "https://github.com/libgit2/libgit2.git")
+    add_versions("v1.3.0", "192eeff84596ff09efb6b01835a066f2df7cd7985e0991c79595688e6b36444e")
+
+    add_deps("cmake")
+    if is_plat("macosx", "iphoneos") then
+        add_frameworks("CoreFoundation", "Security")
+        add_syslinks("iconv", "z")
+    else
+        add_deps("openssl", "zlib")
+    end
+    if is_plat("linux") then
+        add_deps("pcre")
+        add_syslinks("pthread", "dl")
+    elseif is_plat("windows") then
+        add_syslinks("ole32", "rpcrt4", "winhttp")
+    end
+
+    on_install("macosx", "linux", "windows", "android", "iphoneos", function (package)
+        local configs = {"-DBUILD_TESTS=OFF",
+                         "-DBUILD_CLAR=OFF",
+                         "-DBUILD_EXAMPLES=OFF",
+                         "-DBUILD_FUZZERS=OFF",
+                         "-DUSE_SSH=OFF"}
+        table.insert(configs, "-DCMAKE_BUILD_TYPE=" .. (package:debug() and "Debug" or "Release"))
+        table.insert(configs, "-DBUILD_SHARED_LIBS=" .. (package:config("shared") and "ON" or "OFF"))
+        if package:is_plat("android", "iphoneos") then
+            table.insert(configs, "-DUSE_HTTPS=OFF")
+        elseif package:is_plat("windows") then
+            if package:config("vs_runtime"):startswith("MT") then
+                table.insert(configs, "-DSTATIC_CRT=ON")
+            else
+                table.insert(configs, "-DSTATIC_CRT=OFF")
+            end
+            io.replace("CMakeLists.txt", "/GL", "", {plain = true})
+        end
+        import("package.tools.cmake").install(package, configs)
+    end)
+
+    on_test(function (package)
+        assert(package:has_cfuncs("git_repository_init", {includes = "git2.h"}))
+    end)