Handle -iquote in copt

We need to parse copt for -iquote paths and pass them to the include
scanner.  This mirrors what we already do for -I paths.  Note
currently objc_library documentation (see []
recommends use of -iquote while cc_library documentaiton recommends
([]

While we're at it, sanity check the include path, and add/fix a couple
tests.

RELNOTES: None
PiperOrigin-RevId: 268902183

src/main/java/com/google/devtools/build/lib/rules/cpp/CppCompileAction.java

@@ -639,7 +639,23 @@ public CcCompilationContext getCcCompilationContext() {
 
   @Override
   public List<PathFragment> getQuoteIncludeDirs() {
-    return ccCompilationContext.getQuoteIncludeDirs();
+    ImmutableList.Builder<PathFragment> result = ImmutableList.builder();
+    result.addAll(ccCompilationContext.getQuoteIncludeDirs());
+    ImmutableList<String> copts = compileCommandLine.getCopts();
+    for (int i = 0; i < copts.size(); i++) {
+      String opt = copts.get(i);
+      if (opt.startsWith("-iquote")) {
+        if (opt.length() > 7) {
+          result.add(PathFragment.create(opt.substring(7).trim()));
+        } else if (i + 1 < copts.size()) {
+          i++;
+          result.add(PathFragment.create(copts.get(i)));
+        } else {
+          System.err.println("WARNING: dangling -iquote flag in options for " + prettyPrint());
+        }
+      }
+    }
+    return result.build();
   }
 
   @Override
@@ -920,13 +936,11 @@ void verifyActionIncludePaths(List<PathFragment> systemIncludeDirs)
       throws ActionExecutionException {
     ImmutableSet<PathFragment> ignoredDirs = ImmutableSet.copyOf(getValidationIgnoredDirs());
     // We currently do not check the output of:
-    // - getQuoteIncludeDirs(): those only come from includes attributes, and are checked in
-    //   CcCommon.getIncludeDirsFromIncludesAttribute().
     // - getBuiltinIncludeDirs(): while in practice this doesn't happen, bazel can be configured
     //   to use an absolute system root, in which case the builtin include dirs might be absolute.
 
     Iterable<PathFragment> includePathsToVerify =
-        Iterables.concat(getIncludeDirs(), systemIncludeDirs);
+        Iterables.concat(getIncludeDirs(), getQuoteIncludeDirs(), systemIncludeDirs);
     for (PathFragment includePath : includePathsToVerify) {
       // includePathsToVerify contains all paths that are added as -isystem directive on the command
       // line, most of which are added for include directives in the CcCompilationContext and are