Check for LLVM archive writting support by delegating to C.

Author: DiamondLovesYou

src/librustc_llvm/lib.rs

@@ -2109,6 +2109,7 @@ extern {
 
     pub fn LLVMWriteSMDiagnosticToString(d: SMDiagnosticRef, s: RustStringRef);
 
+    pub fn LLVMRustUseArchiveWriter() -> bool;
     pub fn LLVMRustWriteArchive(Dst: *const c_char,
                                 NumMembers: size_t,
                                 Members: *const RustArchiveMemberRef,

src/librustc_trans/back/archive.rs

@@ -218,7 +218,7 @@ impl<'a> ArchiveBuilder<'a> {
     }
 
     pub fn llvm_archive_kind(&self) -> Option<ArchiveKind> {
-        if unsafe { llvm::LLVMVersionMinor() < 7 } {
+        if !unsafe { llvm::LLVMRustUseArchiveWriter() } {
             return None
         }
 

src/rustllvm/ArchiveWrapper.cpp

@@ -36,6 +36,11 @@ typedef Archive RustArchive;
 #define GET_ARCHIVE(a) (a)
 #endif
 
+extern "C" bool
+LLVMRustUseArchiveWriter() {
+  return LLVM_VERSION_MINOR >= 7 && !PNACL_LLVM;
+}
+
 extern "C" void*
 LLVMRustOpenArchive(char *path) {
     ErrorOr<std::unique_ptr<MemoryBuffer>> buf_or = MemoryBuffer::getFile(path,