[Modules] Resolve top-headers of modules lazily.

This allows resolving top-header filenames of modules to FileEntries when
we need them, not eagerly.

Note that that this breaks ABI for libclang functions
clang_Module_getTopLevelHeader / clang_Module_getNumTopLevelHeaders
but this is fine because they are experimental and not widely used yet.

llvm-svn: 176975
diff --git a/clang/tools/c-index-test/c-index-test.c b/clang/tools/c-index-test/c-index-test.c
index 46d61e9..88b49ed 100644
--- a/clang/tools/c-index-test/c-index-test.c
+++ b/clang/tools/c-index-test/c-index-test.c
@@ -1996,12 +1996,12 @@
           unsigned i, numHeaders;
           if (mod) {
             name = clang_Module_getFullName(mod);
-            numHeaders = clang_Module_getNumTopLevelHeaders(mod);
+            numHeaders = clang_Module_getNumTopLevelHeaders(TU, mod);
             printf(" ModuleName=%s Headers(%d):",
                    clang_getCString(name), numHeaders);
             clang_disposeString(name);
             for (i = 0; i < numHeaders; ++i) {
-              CXFile file = clang_Module_getTopLevelHeader(mod, i);
+              CXFile file = clang_Module_getTopLevelHeader(TU, mod, i);
               CXString filename = clang_getFileName(file);
               printf("\n%s", clang_getCString(filename));
               clang_disposeString(filename);