Merging r373049:

------------------------------------------------------------------------
r373049 | hans | 2019-09-27 01:14:45 -0700 (Fri, 27 Sep 2019) | 4 lines

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).
------------------------------------------------------------------------

Author: zmodem

clang/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: