[Flang, Clang] Enable and test 'rdynamic' flag (#75598)

Enable and test 'rdynamic' flag

Author: Radu2k

clang/include/clang/Driver/Options.td

@@ -5308,7 +5308,8 @@ def rewrite_objc : Flag<["-"], "rewrite-objc">, Flags<[NoXarchOption]>,
 def rewrite_legacy_objc : Flag<["-"], "rewrite-legacy-objc">,
   Flags<[NoXarchOption]>,
   HelpText<"Rewrite Legacy Objective-C source to C++">;
-def rdynamic : Flag<["-"], "rdynamic">, Group<Link_Group>;
+def rdynamic : Flag<["-"], "rdynamic">, Group<Link_Group>,
+  Visibility<[ClangOption, FlangOption]>;
 def resource_dir : Separate<["-"], "resource-dir">,
   Flags<[NoXarchOption, HelpHidden]>,
   Visibility<[ClangOption, CC1Option, CLOption, DXCOption]>,

flang/test/Driver/dynamic-linker.f90

@@ -7,13 +7,17 @@
 ! RUN: %flang -### --target=x86_64-windows-msvc -rpath /path/to/dir -shared \
 ! RUN:     -static %s 2>&1 | FileCheck \
 ! RUN:     --check-prefixes=MSVC-LINKER-OPTIONS %s
+! RUN: %flang -### --target=aarch64-linux-none -rdynamic %s 2>&1 | FileCheck --check-prefixes=RDYNAMIC-LINKER-OPTION %s
 
 ! TODO: Could the linker have an extension or a suffix?
 ! GNU-LINKER-OPTIONS: "{{.*}}ld{{(.exe)?}}"
 ! GNU-LINKER-OPTIONS-SAME: "-shared"
 ! GNU-LINKER-OPTIONS-SAME: "-static"
 ! GNU-LINKER-OPTIONS-SAME: "-rpath" "/path/to/dir"
 
+! RDYNAMIC-LINKER-OPTION: "{{.*}}ld"
+! RDYNAMIC-LINKER-OPTION-SAME: "-export-dynamic"
+
 ! For MSVC, adding -static does not add any additional linker options.
 ! MSVC-LINKER-OPTIONS: "{{.*}}link{{(.exe)?}}"
 ! MSVC-LINKER-OPTIONS-SAME: "-dll"