[LLD] [MinGW] Support --out-implib=name in addition to "--out-implib name"

[ruiu]

LGTM

lld/trunk/MinGW/Options.td

def l: JoinedOrSeparate<["-"], "l">, MetaVarName<"<libName>">,
   HelpText<"Root name of library to use">;
 def m: JoinedOrSeparate<["-"], "m">, HelpText<"Set target emulation">;
 def mllvm: S<"mllvm">;
 def no_whole_archive: F<"no-whole-archive">,
     HelpText<"No longer include all object files for following archives">;
 def o: JoinedOrSeparate<["-"], "o">, MetaVarName<"<path>">,
   HelpText<"Path to file to write output">;
 def out_implib: Separate<["--"], "out-implib">, HelpText<"Import library name">;
+def out_implib_eq: Joined<["--"], "out-implib=">, Alias<out_implib>;
 def output_def: S<"output-def">, HelpText<"Output def file">;
 def shared: F<"shared">, HelpText<"Build a shared object">;
 def subs: S<"subsystem">, HelpText<"Specify subsystem">;
 def stack: S<"stack">;
 def whole_archive: F<"whole-archive">,
     HelpText<"Include all object files for following archives">;
 def verbose: F<"verbose">, HelpText<"Verbose mode">;
 

lld/trunk/test/MinGW/driver.test

 RUN: ld.lld -### foo.o -m i386pep -shared FOO.DEF | FileCheck -check-prefix=DEF2 %s
 DEF2: -def:FOO.DEF
 
 RUN: ld.lld -### foo.o -m i386pep -obar.exe | FileCheck -check-prefix=OUT %s
 RUN: ld.lld -### foo.o -m i386pep -o bar.exe | FileCheck -check-prefix=OUT %s
 OUT: -out:bar.exe
 
 RUN: ld.lld -### foo.o -m i386pep --out-implib bar | FileCheck -check-prefix=IMPLIB %s
+RUN: ld.lld -### foo.o -m i386pep --out-implib=bar | FileCheck -check-prefix=IMPLIB %s
 IMPLIB: -implib:bar
 
 RUN: ld.lld -### foo.o -m i386pep -out-implib bar | FileCheck -check-prefix=NOIMPLIB %s
 NOIMPLIB: -out:ut-implib
 
 RUN: ld.lld -### foo.o -m i386pep -e bar | FileCheck -check-prefix=ENTRY %s
 RUN: ld.lld -### foo.o -m i386pep -entry bar | FileCheck -check-prefix=ENTRY %s
 RUN: ld.lld -### foo.o -m i386pep --entry bar | FileCheck -check-prefix=ENTRY %s