configure: Enable libc++ with LLVM with clang

When clang is enabled, also pass through --enable-libcpp to LLVM's configure
command line to help it pick up the most recent c++ runtime library. This also
changes the mklldeps.py script to pick up on whether LLVM was linked against
stdc++ or c++ based on the --cxxflags that llvm-config prints.

In an ongoing attempt to update LLVM, the bots need to update their C compilers
to something that supports c++11 (LLVM recently switched). The OSX bots are
running Lion (10.7), which only supports up to gcc 4.2 and clang 3.2. Apparently
the libstdc++ is too old (even on the most updated command line tools) for LLVM,
but using libc++ instead appears to work just fine.

configure

@@ -938,13 +938,15 @@ do
 
             LLVM_CXX_64="ccache clang++ -Qunused-arguments"
             LLVM_CC_64="ccache clang -Qunused-arguments"
+            LLVM_OPTS="$LLVM_OPTS --enable-libcpp"
             ;;
             ("clang")
             LLVM_CXX_32="clang++ -m32 -Qunused-arguments"
             LLVM_CC_32="clang -m32 -Qunused-arguments"
 
             LLVM_CXX_64="clang++ -Qunused-arguments"
             LLVM_CC_64="clang -Qunused-arguments"
+            LLVM_OPTS="$LLVM_OPTS --enable-libcpp"
             ;;
             ("ccache gcc")
             LLVM_CXX_32="ccache g++ -m32"

src/etc/mklldeps.py

@@ -56,7 +56,7 @@
     f.write("#[cfg(" + ', '.join(cfg) + ")]\n")
 
     # LLVM libs
-    args = [llconfig, '--libs']
+    args = [llconfig, '--libs', '--system-libs']
     args.extend(components)
     proc = subprocess.Popen(args, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
     out, err = proc.communicate()
@@ -65,9 +65,13 @@
         print("failed to run llconfig: args = `{}`".format(args))
         sys.exit(1)
 
-    for lib in out.strip().split(' '):
-        lib = lib[2:] # chop of the leading '-l'
-        f.write("#[link(name = \"" + lib + "\", kind = \"static\")]\n")
+    for lib in out.strip().replace("\n", ' ').split(' '):
+        lib = lib.strip()[2:] # chop of the leading '-l'
+        f.write("#[link(name = \"" + lib + "\"")
+        # LLVM libraries are all static libraries
+        if 'LLVM' in lib:
+            f.write(", kind = \"static\"")
+        f.write(")]\n")
 
     # LLVM ldflags
     args = [llconfig, '--ldflags']
@@ -82,8 +86,19 @@
         if lib[:2] == "-l":
             f.write("#[link(name = \"" + lib[2:] + "\")]\n")
 
-    #extra
-    f.write("#[link(name = \"stdc++\")]\n")
-    if os == 'win32':
-        f.write("#[link(name = \"imagehlp\")]\n")
+    # C++ runtime library
+    args = [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:
+        f.write("#[link(name = \"stdc++\")]\n")
+
+    # Attach everything to an extern block
     f.write("extern {}\n")