[Scons] Added the ability to change the visibility of symbols

(cherry picked from commit f5e4f95cde6de04ed9bf6abfd9bf12cc0bac6b1a)

tools/common_compiler_flags.py

@@ -39,6 +39,14 @@ def generate(env):
     elif env.get("is_msvc", False):
         env.Append(CXXFLAGS=["/EHsc"])
 
+    if not env.get("is_msvc", False):
+        if env["symbols_visibility"] == "visible":
+            env.Append(CCFLAGS=["-fvisibility=default"])
+            env.Append(LINKFLAGS=["-fvisibility=default"])
+        elif env["symbols_visibility"] == "hidden":
+            env.Append(CCFLAGS=["-fvisibility=hidden"])
+            env.Append(LINKFLAGS=["-fvisibility=hidden"])
+
     # Set optimize and debug_symbols flags.
     # "custom" means do nothing and let users set their own optimization flags.
     if env.get("is_msvc", False):

tools/godotcpp.py

@@ -291,6 +291,15 @@ def options(opts, env):
         )
     )
 
+    opts.Add(
+        EnumVariable(
+            key="symbols_visibility",
+            help="Symbols visibility on GNU platforms. Use 'auto' to apply the default value.",
+            default=env.get("symbols_visibility", "hidden"),
+            allowed_values=["auto", "visible", "hidden"],
+        )
+    )
+
     opts.Add(
         EnumVariable(
             "optimize",