Fix build failure when using older crosstool that doesn't have stdc-predef.h.

We used to unconditionally add this file, but that doesn't make sense for crosstools that don't have it. Long-term, we need to get the name of this file from the CROSSTOOL file.

I was unable to test this because getting all of an older crosstool's dependencies into a test was too hard. But I manually verified that it works.

--
MOS_MIGRATED_REVID=90533610

1 files changed, 6 insertions, 3 deletions

diff --git a/src/main/java/com/google/devtools/build/lib/rules/cpp/CppConfiguration.java b/src/main/java/com/google/devtools/build/lib/rules/cpp/CppConfiguration.java
index b3cdf3b82b..9031b721c2 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/cpp/CppConfiguration.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/cpp/CppConfiguration.java
@@ -1749,9 +1749,12 @@ public class CppConfiguration extends BuildConfiguration.Fragment {
     if (getSysroot() != null && !getSysroot().isAbsolute()) {
       Root sysrootRoot = Iterables.getOnlyElement(
           resolver.findPackageRoots(ImmutableList.of(getSysroot())).entrySet()).getValue();
-      builtInIncludeFile = Preconditions.checkNotNull(artifactFactory.getSourceArtifact(
-              sysroot.getRelative(BUILT_IN_INCLUDE_PATH_FRAGMENT), sysrootRoot),
-          "%s %s", sysrootRoot, sysroot);
+      PathFragment sysrootExecPath = sysroot.getRelative(BUILT_IN_INCLUDE_PATH_FRAGMENT);
+      if (sysrootRoot.getPath().getRelative(sysrootExecPath).exists()) {
+        builtInIncludeFile = Preconditions.checkNotNull(
+            artifactFactory.getSourceArtifact(sysrootExecPath, sysrootRoot),
+            "%s %s", sysrootRoot, sysroot);
+      }
     }
     try {
       getFdoSupport().prepareToBuild(execRoot, genfilesPath, artifactFactory, resolver);