SCons: Remove unnecessary $LINK overrides

As of SCons 4.0.1, the default value for $LINK is $SMARTLINK, which itself
is a function that will use $CXX as linker for C++:

https://github.com/SCons/scons/blob/4.0.1/SCons/Tool/link.py#L327-L328
https://github.com/SCons/scons/blob/4.0.1/SCons/Tool/link.py#L54-L76

So we don't need to manually specify the same value as $CXX for $LINK.

(cherry picked from commit 2e4bff1cfea3843953a176656490339305a2c779)

platform/javascript/detect.py

@@ -107,7 +107,6 @@ def configure(env):
 
     env["CC"] = "emcc"
     env["CXX"] = "em++"
-    env["LINK"] = "emcc"
 
     env["AR"] = "emar"
     env["RANLIB"] = "emranlib"

platform/osx/detect.py

@@ -97,7 +97,6 @@ def configure(env):
             mpprefix = os.environ.get("MACPORTS_PREFIX", "/opt/local")
             mpclangver = env["macports_clang"]
             env["CC"] = mpprefix + "/libexec/llvm-" + mpclangver + "/bin/clang"
-            env["LINK"] = mpprefix + "/libexec/llvm-" + mpclangver + "/bin/clang++"
             env["CXX"] = mpprefix + "/libexec/llvm-" + mpclangver + "/bin/clang++"
             env["AR"] = mpprefix + "/libexec/llvm-" + mpclangver + "/bin/llvm-ar"
             env["RANLIB"] = mpprefix + "/libexec/llvm-" + mpclangver + "/bin/llvm-ranlib"

platform/windows/detect.py

@@ -354,18 +354,17 @@ def configure_mingw(env):
 
     if env["use_llvm"]:
         env["CC"] = mingw_prefix + "clang"
-        env["AS"] = mingw_prefix + "as"
         env["CXX"] = mingw_prefix + "clang++"
+        env["AS"] = mingw_prefix + "as"
         env["AR"] = mingw_prefix + "ar"
         env["RANLIB"] = mingw_prefix + "ranlib"
-        env["LINK"] = mingw_prefix + "clang++"
     else:
         env["CC"] = mingw_prefix + "gcc"
-        env["AS"] = mingw_prefix + "as"
         env["CXX"] = mingw_prefix + "g++"
+        env["AS"] = mingw_prefix + "as"
         env["AR"] = mingw_prefix + "gcc-ar"
         env["RANLIB"] = mingw_prefix + "gcc-ranlib"
-        env["LINK"] = mingw_prefix + "g++"
+
     env["x86_libtheora_opt_gcc"] = True
 
     if env["use_lto"]: