mail/thunderbird: fix linking with libc++18

copied from www/firefox

PR:		276746
(cherry picked from commit 560d828)

mail/thunderbird/files/patch-bug1874059

@@ -0,0 +1,25 @@
+commit 56c888446600991803fd92d668349101ad4bf160
+Author: Christoph Moench-Tegeder <cmt@burggraben.net>
+Date:   Tue Feb 6 22:51:27 2024 +0100
+
+    switch to -fvisibility flags
+
+    this fixes linkage with llvm18 (which does not like the former
+    approach via the #pragma in gcc_hidden.h
+
+    PR: 276746
+    Submitted by: dim@
+
+diff --git build/moz.configure/toolchain.configure build/moz.configure/toolchain.configure
+index d08b748db250..4696f69153f6 100644
+--- build/moz.configure/toolchain.configure
++++ build/moz.configure/toolchain.configure
+@@ -2186,7 +2186,7 @@ set_define("_LIBCPP_HIDE_FROM_ABI", libcxx_override_visibility.hide_from_abi)
+ @depends(target, build_environment)
+ def visibility_flags(target, env):
+     if target.os != "WINNT":
+-        if target.kernel == "Darwin":
++        if target.kernel == "Darwin" or target.kernel == "FreeBSD":
+             return ("-fvisibility=hidden", "-fvisibility-inlines-hidden")
+         return (
+             "-I%s/system_wrappers" % os.path.join(env.dist),