[Flang][Driver] Enable the -B option (#109965)

The option provides the search prefix for executables, libraries and
data files.

The option is implemented in the common portion of the Driver and only
needs to be enabled in Flang. Test added is a copy of the relevant test
in Clang.

Author: kiranchandramohan

clang/include/clang/Driver/Options.td

@@ -816,6 +816,7 @@ def _DASH_DASH : Option<["--"], "", KIND_REMAINING_ARGS>,
 def A : JoinedOrSeparate<["-"], "A">, Flags<[RenderJoined]>,
   Group<gfortran_Group>;
 def B : JoinedOrSeparate<["-"], "B">, MetaVarName<"<prefix>">,
+    Visibility<[ClangOption, FlangOption]>,
     HelpText<"Search $prefix$file for executables, libraries, and data files. "
     "If $prefix is a directory, search $prefix/$file">;
 def gcc_install_dir_EQ : Joined<["--"], "gcc-install-dir=">,

flang/test/Driver/B-opt.f90

@@ -0,0 +1,23 @@
+! Check -B driver option.
+!
+! Target triple prefix is not detected for -B.
+! RUN: %flang %s -### -o %t.o --target=i386-unknown-linux \
+! RUN:     -B %S/Inputs/B_opt_tree/dir1 -fuse-ld=ld 2>&1 \
+! RUN:   | FileCheck --check-prefix=CHECK-B-OPT-TRIPLE %s
+! CHECK-B-OPT-TRIPLE-NOT: "{{.*}}/Inputs/B_opt_tree/dir1{{/|\\\\}}i386-unknown-linux-ld"
+!
+! RUN: %flang %s -### -o %t.o --target=i386-unknown-linux \
+! RUN:     -B %S/Inputs/B_opt_tree/dir2 -fuse-ld=ld 2>&1 \
+! RUN:   | FileCheck --check-prefix=CHECK-B-OPT-DIR %s
+! CHECK-B-OPT-DIR: "{{.*}}/Inputs/B_opt_tree/dir2{{/|\\\\}}ld"
+!
+! RUN: %flang %s -### -o %t.o --target=i386-unknown-linux \
+! RUN:     -B %S/Inputs/B_opt_tree/dir3/prefix- -fuse-ld=ld 2>&1 \
+! RUN:   | FileCheck --check-prefix=CHECK-B-OPT-PREFIX %s
+! CHECK-B-OPT-PREFIX: "{{.*}}/Inputs/B_opt_tree/dir3{{/|\\\\}}prefix-ld"
+!
+! RUN: %flang %s -### -o %t.o --target=i386-unknown-linux \
+! RUN:     -B %S/Inputs/B_opt_tree/dir3/prefix- \
+! RUN:     -B %S/Inputs/B_opt_tree/dir2 2>&1 -fuse-ld=ld \
+! RUN:   | FileCheck --check-prefix=CHECK-B-OPT-MULT %s
+! CHECK-B-OPT-MULT: "{{.*}}/Inputs/B_opt_tree/dir3{{/|\\\\}}prefix-ld"