[COFF] Don't error out on undefined references to __enclave_config

This is required for linking the CRT from MSVC 2017 15.5.

Differential Revision: https://reviews.llvm.org/D41089

llvm-svn: 320462

lld/COFF/Driver.cpp

@@ -1167,6 +1167,8 @@ void LinkerDriver::link(ArrayRef<const char *> ArgsArr) {
   Symtab->addAbsolute(mangle("__guard_iat_table"), 0);
   Symtab->addAbsolute(mangle("__guard_longjmp_count"), 0);
   Symtab->addAbsolute(mangle("__guard_longjmp_table"), 0);
+  // Needed for MSVC 2017 15.5 CRT.
+  Symtab->addAbsolute(mangle("__enclave_config"), 0);
 
   // This code may add new undefined symbols to the link, which may enqueue more
   // symbol resolution tasks, so we need to continue executing tasks until we

lld/test/COFF/guardcf.test

@@ -71,4 +71,10 @@ symbols:
     SimpleType:      IMAGE_SYM_TYPE_NULL
     ComplexType:     IMAGE_SYM_DTYPE_NULL
     StorageClass:    IMAGE_SYM_CLASS_EXTERNAL
+  - Name:            __enclave_config
+    Value:           0
+    SectionNumber:   0
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_NULL
+    StorageClass:    IMAGE_SYM_CLASS_EXTERNAL
 ...