Ignore -ffile-compilation-dir when processing swift modules.

Author: qiongsiwu

lib/Basic/LangOptions.cpp

@@ -734,10 +734,11 @@ namespace {
         "-working-directory=",
         "-working-directory"};
 
-  constexpr std::array<std::string_view, 15>
+  constexpr std::array<std::string_view, 16>
       knownClangDependencyIgnorablePrefiexes = {"-I",
                                                 "-F",
                                                 "-fmodule-map-file=",
+                                                "-ffile-compilation-dir",
                                                 "-iquote",
                                                 "-idirafter",
                                                 "-iframeworkwithsysroot",

test/ScanDependencies/eliminate_unused_vfs.swift

@@ -6,7 +6,7 @@
 
 // RUN: sed -e "s|OUT_DIR|%t/redirects|g"  -e "s|IN_DIR|%S/Inputs/CHeaders|g" %t/overlay_template.yaml > %t/overlay.yaml
 
-// RUN: %target-swift-frontend -scan-dependencies -module-load-mode prefer-interface -module-cache-path %t/module-cache %t/test.swift -o %t/deps.json -I %S/Inputs/CHeaders -I %S/Inputs/Swift -disable-implicit-concurrency-module-import -disable-implicit-string-processing-module-import -Xcc -ivfsoverlay -Xcc %t/overlay.yaml
+// RUN: %target-swift-frontend -scan-dependencies -module-load-mode prefer-interface -module-cache-path %t/module-cache %t/test.swift -o %t/deps.json -I %S/Inputs/CHeaders -I %S/Inputs/Swift -disable-implicit-concurrency-module-import -disable-implicit-string-processing-module-import -file-compilation-dir %t -Xcc -ivfsoverlay -Xcc %t/overlay.yaml
 // RUN: %validate-json %t/deps.json | %FileCheck %s
 
 //--- overlay_template.yaml
@@ -54,6 +54,7 @@ import F
 // CHECK: "-compile-module-from-interface"
 // CHECK-NOT: "-ivfsoverlay",
 // CHECK-NOT: "{{.*}}{{/|\\}}preserve_used_vfs.swift.tmp{{/|\\}}overlay.yaml",
+// CHECK-NOT: "-ffile-compilation-dir={{.*}}"
 // CHECK: ],
 
 /// --------Clang module F