!131 [clang] Set default prefix for search path when prefix is empty

From: @luofeng14 
Reviewed-by: @cf-zhao 
Signed-off-by: @cf-zhao

Author: openeuler-ci-bot

clang/lib/Driver/ToolChains/Clang.cpp

@@ -4689,6 +4689,12 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
 #ifdef BUILD_FOR_OPENEULER
   if (Args.hasFlag(options::OPT_fgcc_compatible,
                    options::OPT_fno_gcc_compatible, false)) {
+    if (Args.hasArg(options::OPT_nostdinc) && !Args.hasArg(options::OPT_iprefix)) {
+      SmallString<128> P(D.ResourceDir);
+      P += llvm::sys::path::get_separator();
+      CmdArgs.insert(CmdArgs.begin() + 1, "-iprefix");
+      CmdArgs.insert(CmdArgs.begin() + 2, Args.MakeArgString(P));
+    }
     // compatibility relevent warnings
     CmdArgs.push_back("-Wno-error=unknown-warning-option");
     CmdArgs.push_back("-Wno-error=ignored-attributes");

clang/test/Driver/prefix.c

@@ -0,0 +1,14 @@
+// REQUIRES: build_for_openeuler
+
+// RUN: %clang  %s
+// RUN: %clang  -iprefix $(dirname `which clang`)/../lib/clang/*/   -iwithprefix  include %s
+// RUN: %clang  -iwithprefix include %s
+// RUN: %clang  -nostdinc -iwithprefix include %s -fgcc-compatible
+// RUN: %clang  -nostdinc -iprefix $(dirname `which clang`)/../lib/clang/*/ -iwithprefix  include %s -fgcc-compatible
+// RUN: not %clang -nostdinc   -iwithprefix  include %s
+// RUN: not %clang -nostdinc  -iprefix ""  -iwithprefix  include %s
+
+#include <stdarg.h>
+int main(void) {
+return 0;
+}