[LLD] [MinGW] Allow linking to DLLs directly

[mstorsjo]

Summary

As the COFF linker is capable of linking directly against a DLL now
(after D104530, as long as it is running in mingw mode), don't error
out here but successfully load libraries specified with "-l" from DLLs
if that's what ld.bfd would have matched.

[mstorsjo]

Updated to rerun CI after fixing a test in the base patch

[mati865]

LGTM once D104530 is merged.

lld/MinGW/Driver.cpp

if (!bStatic) {
       if (Optional<std::string> s = findFile(dir, name + ".dll.a"))
         return *s;
     }
     if (Optional<std::string> s = findFile(dir, "lib" + name + ".a"))
       return *s;
     if (!bStatic) {
       if (Optional<std::string> s = findFile(dir, name + ".lib"))
         return *s;
-      if (Optional<std::string> s = findFile(dir, "lib" + name + ".dll")) {
-        error("lld doesn't support linking directly against " + *s +
-              ", use an import library");
-        return "";
-      }
-      if (Optional<std::string> s = findFile(dir, name + ".dll")) {
-        error("lld doesn't support linking directly against " + *s +
-              ", use an import library");
-        return "";
-      }
+      if (Optional<std::string> s = findFile(dir, "lib" + name + ".dll"))
+        return *s;
+      if (Optional<std::string> s = findFile(dir, name + ".dll"))
+        return *s;
     }
   }
   error("unable to find library -l" + name);
   return "";
 }
 
 // Convert Unix-ish command line arguments to Windows-ish ones and
 // then call coff::link.

lld/test/MinGW/lib.test

 RUN: echo > %t/lib/noprefix.dll.a
 RUN: echo > %t/lib/msvcstyle.lib
 RUN: ld.lld -### -m i386pep -L%t/lib -lnoprefix -lmsvcstyle 2>&1 | FileCheck -check-prefix=OTHERSTYLES %s
 OTHERSTYLES: noprefix.dll.a
 OTHERSTYLES-SAME: msvcstyle.lib
 
 RUN: echo > %t/lib/libnoimplib.dll
 RUN: echo > %t/lib/noprefix_noimplib.dll
-RUN: not ld.lld -### -m i386pep -L%t/lib -lnoimplib 2>&1 | FileCheck -check-prefix=UNSUPPORTED-DLL1 %s
-RUN: not ld.lld -### -m i386pep -L%t/lib -lnoprefix_noimplib 2>&1 | FileCheck -check-prefix=UNSUPPORTED-DLL2 %s
-UNSUPPORTED-DLL1: lld doesn't support linking directly against {{.*}}libnoimplib.dll, use an import library
-UNSUPPORTED-DLL2: lld doesn't support linking directly against {{.*}}noprefix_noimplib.dll, use an import library
+RUN: ld.lld -### -m i386pep -L%t/lib -lnoimplib 2>&1 | FileCheck -check-prefix=DLL1 %s
+RUN: ld.lld -### -m i386pep -L%t/lib -lnoprefix_noimplib 2>&1 | FileCheck -check-prefix=DLL2 %s
+DLL1: libnoimplib.dll
+DLL2: noprefix_noimplib.dll