librustc: add LLVM LDFLAGS to deps

This commit let librustc automatically pickup LDFLAGS dependencies
inherited from LLVM, which may otherwise result in undefined
references to external symbols under certain linking environment.

A symptom of this issue is eg. a failure when trying to link against
librustc (due to unresolved ffi_*i symbols), while using a system-wide
LLVM.

Signed-off-by: Luca Bruno <lucab@debian.org>

src/etc/mklldeps.py

@@ -55,6 +55,7 @@ for llconfig in sys.argv[3:]:
 
     f.write("#[cfg(" + ', '.join(cfg) + ")]\n")
 
+    # LLVM libs
     args = [llconfig, '--libs']
     args.extend(components)
     proc = subprocess.Popen(args, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
@@ -67,6 +68,21 @@ for llconfig in sys.argv[3:]:
     for lib in out.strip().split(' '):
         lib = lib[2:] # chop of the leading '-l'
         f.write("#[link(name = \"" + lib + "\", kind = \"static\")]\n")
+
+    # LLVM ldflags
+    args = [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")
+
+    #extra
     f.write("#[link(name = \"stdc++\")]\n")
     if os == 'win32':
         f.write("#[link(name = \"imagehlp\")]\n")