etc: The --system-libs flag is LLVM 3.5+

Older version of LLVM did not have this flag, so we need to fall back to our
previous library detection when using older versions of LLVM.

src/etc/mklldeps.py

@@ -31,11 +31,20 @@ f.write("""// Copyright 2013 The Rust Project Developers. See the COPYRIGHT
 //          take a look at src/etc/mklldeps.py if you're interested
 """)
 
+def run(args):
+    proc = subprocess.Popen(args, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
+    out, err = proc.communicate()
+
+    if err:
+        print("failed to run llconfig: args = `{}`".format(args))
+        print(err)
+        sys.exit(1)
+    return out
+
 for llconfig in sys.argv[3:]:
     f.write("\n")
 
-    proc = subprocess.Popen([llconfig, '--host-target'], stdout = subprocess.PIPE)
+    out = run([llconfig, '--host-target'])
-    out, err = proc.communicate()
     arch, os = out.split('-', 1)
     arch = 'x86' if arch == 'i686' or arch == 'i386' else arch
     if 'darwin' in os:
@@ -55,16 +64,15 @@ for llconfig in sys.argv[3:]:
 
     f.write("#[cfg(" + ', '.join(cfg) + ")]\n")
 
+    version = run([llconfig, '--version']).strip()
+
     # LLVM libs
+    if version < '3.5':
+      args = [llconfig, '--libs']
+    else:
       args = [llconfig, '--libs', '--system-libs']
     args.extend(components)
-    proc = subprocess.Popen(args, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
+    out = run(args)
-    out, err = proc.communicate()
-
-    if err:
-        print("failed to run llconfig: args = `{}`".format(args))
-        sys.exit(1)
-
     for lib in out.strip().replace("\n", ' ').split(' '):
         lib = lib.strip()[2:] # chop of the leading '-l'
         f.write("#[link(name = \"" + lib + "\"")
@@ -73,28 +81,19 @@ for llconfig in sys.argv[3:]:
             f.write(", kind = \"static\"")
         f.write(")]\n")
 
+    # llvm-config before 3.5 didn't have a system-libs flag
+    if version < '3.5':
+      if os == 'win32':
+        f.write("#[link(name = \"imagehlp\")]")
+
     # LLVM ldflags
-    args = [llconfig, '--ldflags']
+    out = run([llconfig, '--ldflags'])
-    proc = subprocess.Popen(args, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
-    out, err = proc.communicate()
-
-    if err:
-        print("failed to run llconfig: args = `{}`".format(args))
-        sys.exit(1)
-
     for lib in out.strip().split(' '):
         if lib[:2] == "-l":
             f.write("#[link(name = \"" + lib[2:] + "\")]\n")
 
     # C++ runtime library
-    args = [llconfig, '--cxxflags']
+    out = run([llconfig, '--cxxflags'])
-    proc = subprocess.Popen(args, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
-    out, err = proc.communicate()
-
-    if err:
-        print("failed to run llconfig: args = `{}`".format(args))
-        sys.exit(1)
-
     if 'stdlib=libc++' in out:
         f.write("#[link(name = \"c++\")]\n")
     else: