Fix the 'directory' field in DumpCompilationDatabase and add test

This broke in r371027 due to a missing negation
(llvm::sys::fs::current_path returns false on success).

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@373049 91177308-0d34-0410-b5e6-96231b3b80d8
(cherry picked from commit 0f7791e)

lib/Driver/ToolChains/Clang.cpp

@@ -2016,7 +2016,7 @@ void Clang::DumpCompilationDatabase(Compilation &C, StringRef Filename,
   }
   auto &CDB = *CompilationDatabase;
   SmallString<128> Buf;
-  if (!llvm::sys::fs::current_path(Buf))
+  if (llvm::sys::fs::current_path(Buf))
     Buf = ".";
   CDB << "{ \"directory\": \"" << escape(Buf) << "\"";
   CDB << ", \"file\": \"" << escape(Input.getFilename()) << "\"";

test/Driver/compilation_database.c

@@ -1,8 +1,8 @@
-// RUN: mkdir -p %t && cd %t
+// RUN: mkdir -p %t.workdir && cd %t.workdir
 // RUN: %clang -MD -MP --sysroot=somewhere -c -x c %s -xc++ %s -Wall -MJ - -no-canonical-prefixes 2>&1 | FileCheck %s
 // RUN: not %clang -c -x c %s -MJ %s/non-existant -no-canonical-prefixes 2>&1 | FileCheck --check-prefix=ERROR %s
 
-// CHECK: { "directory": "{{.*}}",  "file": "[[SRC:[^"]+[/|\\]compilation_database.c]]", "output": "compilation_database.o", "arguments": ["{{[^"]*}}clang{{[^"]*}}", "-xc", "[[SRC]]", "--sysroot=somewhere", "-c", "-Wall",{{.*}} "--target={{[^"]+}}"]},
+// CHECK: { "directory": "{{[^"]*}}workdir",  "file": "[[SRC:[^"]+[/|\\]compilation_database.c]]", "output": "compilation_database.o", "arguments": ["{{[^"]*}}clang{{[^"]*}}", "-xc", "[[SRC]]", "--sysroot=somewhere", "-c", "-Wall",{{.*}} "--target={{[^"]+}}"]},
 // CHECK: { "directory": "{{.*}}",  "file": "[[SRC:[^"]+[/|\\]compilation_database.c]]", "output": "compilation_database.o", "arguments": ["{{[^"]*}}clang{{[^"]*}}", "-xc++", "[[SRC]]", "--sysroot=somewhere", "-c", "-Wall",{{.*}} "--target={{[^"]+}}"]},
 // ERROR: error: compilation database '{{.*}}/non-existant' could not be opened: