SConscript.boot do not recognize clang++ compiler if not given by name.

[mazhe]

Hello,

I'm trying to build swift on a FreeBSD system, and one of my issues is that the SConscript.boot code try to identify compiler by executable basename:

swift/BuildTools/SCons/SConscript.boot

Line 348 in c5ff370

if os.path.basename(env["CXX"]).startswith(("clang", "clang++")) :

First, accepting "clang" as a valid C++ compiler when it's the C driver is a bit weird, and this will obviously won't work if clang++ is used under any other valid name such as c++ or clang++50 etc. I'm not sure how scons usually work out compilers IDs, but in this case the only way I see would be to get it from a "$CXX -v" invokation, what would you think of the following?

--- BuildTools/SCons/SConscript.boot.orig	2017-11-28 12:51:50 UTC
+++ BuildTools/SCons/SConscript.boot
@@ -1,4 +1,4 @@
-import sys, os, re, platform, hashlib
+import sys, os, re, platform, hashlib, subprocess
 sys.path.append(Dir("#/BuildTools/SCons").abspath)
 
 ################################################################################
@@ -343,7 +343,9 @@ elif env["PLATFORM"] == "sunos" :
     #env.Append(CXXFLAGS = ["-z verbose"])
     pass
 else :
-    if os.path.basename(env["CXX"]).startswith(("clang", "clang++")) :
+    cxx_p = subprocess.Popen([os.path.basename(env["CXX"]),"-v"], stderr=subprocess.PIPE)
+    cxx_id = cxx_p.communicate()[1]
+    if "clang" in cxx_id:
         env.Append(CXXFLAGS = [
             "-Weverything",
             "-Wno-unknown-warning-option", # To stay compatible between CLang versions

Thanks for that promising client & keep up the work!