[flang][Driver] Support -Xlinker in flang (#107472)

Partially addresses: #89888

Author: tarunprabhu

clang/include/clang/Driver/Options.td

@@ -1051,6 +1051,7 @@ def z : Separate<["-"], "z">, Flags<[LinkerInput]>,
 def offload_link : Flag<["--"], "offload-link">, Group<Link_Group>,
   HelpText<"Use the new offloading linker to perform the link job.">;
 def Xlinker : Separate<["-"], "Xlinker">, Flags<[LinkerInput, RenderAsInput]>,
+  Visibility<[ClangOption, CLOption, FlangOption, DXCOption]>,
   HelpText<"Pass <arg> to the linker">, MetaVarName<"<arg>">,
   Group<Link_Group>;
 def Xoffload_linker : JoinedAndSeparate<["-"], "Xoffload-linker">,

flang/test/Driver/xlinker.f90

@@ -0,0 +1,21 @@
+! RUN: %flang -### --target=ppc64le-linux-gnu -Xlinker -rpath -Xlinker /not/a/real/path %s 2>&1 | FileCheck %s --check-prefixes=UNIX
+! RUN: %flang -### --target=aarch64-apple-darwin -Xlinker -rpath -Xlinker /not/a/real/path %s 2>&1 | FileCheck %s --check-prefixes=UNIX
+! RUN: %flang -### --target=sparc-sun-solaris2.11 -Xlinker -rpath -Xlinker /not/a/real/path %s 2>&1 | FileCheck %s --check-prefixes=UNIX
+! RUN: %flang -### --target=x86_64-unknown-freebsd -Xlinker -rpath -Xlinker /not/a/real/path %s 2>&1 | FileCheck %s --check-prefixes=UNIX
+! RUN: %flang -### --target=x86_64-unknown-netbsd -Xlinker -rpath -Xlinker /not/a/real/path %s 2>&1 | FileCheck %s --check-prefixes=UNIX
+! RUN: %flang -### --target=x86_64-unknown-openbsd -Xlinker -rpath -Xlinker /not/a/real/path %s 2>&1 | FileCheck %s --check-prefixes=UNIX
+! RUN: %flang -### --target=x86_64-unknown-dragonfly -Xlinker -rpath -Xlinker /not/a/real/path %s 2>&1 | FileCheck %s --check-prefixes=UNIX
+! RUN: %flang -### --target=x86_64-unknown-haiku %s -Xlinker -rpath -Xlinker /not/a/real/path 2>&1 | FileCheck %s --check-prefixes=UNIX
+! RUN: %flang -### --target=x86_64-windows-gnu -Xlinker -rpath -Xlinker /not/a/real/path %s 2>&1 | FileCheck %s --check-prefixes=UNIX
+! RUN: %flang -### --target=aarch64-windows-msvc -Xlinker -rpath -Xlinker /not/a/real/path -o obscure.exe %s 2>&1 | FileCheck %s --check-prefixes=MSVC
+
+! UNIX-LABEL: "{{.*}}ld{{(\.exe)?}}"
+! UNIX-SAME: "-rpath" "/not/a/real/path"
+
+! The name of this file contains the word "link" which results in a match on
+! the compiler line as well. Instead look for the final name of the executable
+! to be created since that will only appear in the linker line.
+! MSVC: -out:obscure.exe
+! MSVC-SAME: "-rpath" "/not/a/real/path"
+
+end program