fix protobuf-c (#260)

* improve protobuf

* Update xmake.lua

packages/p/protobuf-c/xmake.lua

@@ -24,12 +24,38 @@ package("protobuf-c")
 
     on_install("windows", function (package)
         os.cd("build-cmake")
-        import("package.tools.cmake").install(package, {"-Dprotobuf_BUILD_PROTOC_BINARIES=ON"})
+        local cflags
+        local shflags
+        local configs = {}
+        if package:config("shared") then
+            table.insert(configs, "-DBUILD_SHARED_LIBS=ON")
+            cflags = {"-DPROTOBUF_C_USE_SHARED_LIB", "-DPROTOBUF_C_EXPORT"}
+            shflags = "/export:protobuf_c_empty_string"
+        else
+            table.insert(configs, "-DBUILD_SHARED_LIBS=OFF")
+        end
+        if package:config("vs_runtime"):startswith("MT") then
+            table.insert(configs, "-DMSVC_STATIC_BUILD=ON")
+        else
+            table.insert(configs, "-DMSVC_STATIC_BUILD=OFF")
+        end
+        import("package.tools.cmake").install(package, configs, {cflags = cflags, shflags = shflags})
         os.cp("build_*/Release/protoc-gen-c.exe", path.join(package:installdir("bin"), "protoc-c.exe"))
     end)
 
     on_install("linux", "macosx", function (package)
-        import("package.tools.autoconf").install(package, {"--enable-shared=no"})
+        local configs = {}
+        if package:config("pic") ~= false then
+            table.insert(configs, "--with-pic")
+        end
+        if package:config("shared") then
+            table.insert(configs, "--enable-shared=yes")
+            table.insert(configs, "--enable-static=no")
+        else
+            table.insert(configs, "--enable-static=yes")
+            table.insert(configs, "--enable-shared=no")
+        end
+        import("package.tools.autoconf").install(package, configs)
     end)
 
     on_test(function (package)