Create import libraries with empty exports and make sure that archive symbols
are properly populated.

RUN: split-file %s %t.dir && cd %t.dir

RUN: llvm-lib -machine:arm64 -out:arm64.lib -def:test.def
RUN: llvm-nm --print-armap arm64.lib | FileCheck --check-prefixes=CHECK,NOECMAP %s

RUN: llvm-lib -machine:arm64ec -out:arm64ec.lib -def:test.def
RUN: llvm-nm --print-armap arm64ec.lib | FileCheck --check-prefixes=CHECK,ECMAP %s

CHECK:      Archive map
CHECK-NEXT: __IMPORT_DESCRIPTOR_test in test.dll
CHECK-NEXT: __NULL_IMPORT_DESCRIPTOR in test.dll
CHECK-NEXT: test_NULL_THUNK_DATA in test.dll
CHECK-EMPTY:

ECMAP:      Archive EC map
ECMAP-NEXT: __IMPORT_DESCRIPTOR_test in test.dll
ECMAP-NEXT: __NULL_IMPORT_DESCRIPTOR in test.dll
ECMAP-NEXT: test_NULL_THUNK_DATA in test.dll

NOECMAP-NOT: Archive EC map

#--- test.def
LIBRARY test.dll
EXPORTS