When the ASTImporter imports a source location, it avoids importing macro
expansions by calling getSpellingLoc(). That's great in most cases, but for
macros defined in the '<built-in>' source file, the source file is invalid
and does not import correctly, causing an assertion failure (the assertion
is Invalid SLocOffset or bad function choice).

A more reliable way to avoid this is to use getFileLoc(), which does not
return built-in locations. This avoids the crash but still preserves valid
source locations.

I've added a testcase that covers the previously crashing scenario.

https://reviews.llvm.org/D26054

llvm-svn: 286144
diff --git a/clang/test/ASTMerge/Inputs/macro.modulemap b/clang/test/ASTMerge/Inputs/macro.modulemap
new file mode 100644
index 0000000..dba1f22
--- /dev/null
+++ b/clang/test/ASTMerge/Inputs/macro.modulemap
@@ -0,0 +1,4 @@
+module macro1 [extern_c] {
+  header "macro1.h"
+  export *
+}
diff --git a/clang/test/ASTMerge/Inputs/macro1.h b/clang/test/ASTMerge/Inputs/macro1.h
new file mode 100644
index 0000000..f089e61
--- /dev/null
+++ b/clang/test/ASTMerge/Inputs/macro1.h
@@ -0,0 +1,5 @@
+typedef void *VoidRef;
+
+void maybeNull(
+  int i,
+  __nullable VoidRef *__nullable);
diff --git a/clang/test/ASTMerge/Inputs/macro1.m b/clang/test/ASTMerge/Inputs/macro1.m
new file mode 100644
index 0000000..2612613
--- /dev/null
+++ b/clang/test/ASTMerge/Inputs/macro1.m
@@ -0,0 +1,5 @@
+@import macro1;
+
+void foo() {
+  maybeNull(0, 0);
+}
diff --git a/clang/test/ASTMerge/Inputs/macro2.m b/clang/test/ASTMerge/Inputs/macro2.m
new file mode 100644
index 0000000..b5b155a
--- /dev/null
+++ b/clang/test/ASTMerge/Inputs/macro2.m
@@ -0,0 +1,5 @@
+void foo();
+
+void bar() {
+  foo();
+}
diff --git a/clang/test/ASTMerge/macro.m b/clang/test/ASTMerge/macro.m
new file mode 100644
index 0000000..77e596d
--- /dev/null
+++ b/clang/test/ASTMerge/macro.m
@@ -0,0 +1,6 @@
+// RUN: rm -rf %t
+// RUN: mkdir -p %t/cache
+// RUN: %clang_cc1 -fmodules -fmodules-cache-path=%t/cache -fmodule-map-file=%S/Inputs/macro.modulemap -I%S/Inputs -emit-pch -o %t.1.ast %S/Inputs/macro1.m
+// RUN: %clang_cc1 -fmodules -fmodules-cache-path=%t/cache -fmodule-map-file=%S/Inputs/macro.modulemap -I%S/Inputs -emit-pch -o %t.2.ast %S/Inputs/macro2.m
+// RUN: %clang_cc1 -fmodules -ast-merge %t.1.ast -ast-merge %t.2.ast -fsyntax-only -verify %s
+// expected-no-diagnostics