Add libopus (#210)

* Add libopus

* libopus: Disable stack protection on MinGW

packages/l/libopus/patches/1.3.1/cmake.patch

@@ -0,0 +1,12 @@
+diff --git a/CMakeLists.txt b/CMakeLists.txt
+index 17ee3fc2..9027d073 100644
+--- a/CMakeLists.txt
++++ b/CMakeLists.txt
+@@ -16,7 +16,6 @@ string(REGEX
+ message(STATUS "Opus project version: ${PROJECT_VERSION}")
+ 
+ project(Opus LANGUAGES C VERSION ${PROJECT_VERSION})
+-include(opus_buildtype.cmake)
+ 
+ option(OPUS_STACK_PROTECTOR "Use stack protection" ON)
+ option(OPUS_USE_ALLOCA "Use alloca for stack arrays (on non-C99 compilers)" OFF)

packages/l/libopus/xmake.lua

@@ -0,0 +1,28 @@
+package("libopus")
+
+    set_homepage("https://opus-codec.org")
+    set_description("Modern audio compression for the internet.")
+
+    set_urls("https://archive.mozilla.org/pub/opus/opus-$(version).tar.gz",
+             "https://gitlab.xiph.org/xiph/opus.git")
+
+    add_versions("1.3.1", "65b58e1e25b2a114157014736a3d9dfeaad8d41be1c8179866f144a2fb44ff9d")
+    add_patches("1.3.1", path.join(os.scriptdir(), "patches", "1.3.1", "cmake.patch"), "79fba5086d7747d0441f7f156b88e932b662e2d2ccd825279a5a396a2840d3a2")
+
+    add_deps("cmake")
+
+    on_install("windows", "linux", "macosx", "iphoneos", "mingw", "android", function (package)
+        local configs = {}
+        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"))
+        table.insert(configs, "-DCMAKE_POSITION_INDEPENDENT_CODE=ON")
+        if package:is_plat("mingw") then
+            -- Disable stack protection on MinGW since it causes link errors
+            table.insert(configs, "-DOPUS_STACK_PROTECTOR=OFF")
+        end
+        import("package.tools.cmake").install(package, configs)
+    end)
+
+    on_test(function (package)
+        assert(package:has_cfuncs("opus_encoder_create", {includes = "opus/opus.h"}))
+    end)