cmd/link: use libmsvcrt.a during internal link

When using recent versions of gcc with cgo, internal link fails with

c:\>go test debug/pe
--- FAIL: TestInternalLinkerDWARF (0.94s)
    file_test.go:394: building test executable for linktype 2 failed: exit status 2 # command-line-arguments
        runtime/cgo(.text): relocation target __acrt_iob_func not defined for ABI0 (but is defined for ABI0)
        runtime/cgo(.text): relocation target __acrt_iob_func not defined for ABI0 (but is defined for ABI0)
        runtime/cgo(.text): relocation target __acrt_iob_func not defined for ABI0 (but is defined for ABI0)
FAIL
FAIL    debug/pe        4.572s
FAIL

It appears that __acrt_iob_func is defined in libmsvcrt.a. And this
change adds libmsvcrt.a to the list of libraries always used byi
internal linker.

libmsvcrt.a also implements __imp___acrt_iob_func. So this change
also prevents rewriting __imp___acrt_iob_func name into
__acrt_iob_func, otherwise we end up with duplicate __acrt_iob_func
symbol error.

Fixes #23649

Change-Id: Ie9864cd17e907501e9a8a3672bbc33e02ca20e5c
Reviewed-on: https://go-review.googlesource.com/c/go/+/197977
Run-TryBot: Alex Brainman <alex.brainman@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/cmd/link/internal/ld/lib.go

@@ -582,6 +582,11 @@ func (ctxt *Link) loadlib() {
 				if p := ctxt.findLibPath("libmingw32.a"); p != "none" {
 					hostArchive(ctxt, p)
 				}
+				// Link libmsvcrt.a to resolve '__acrt_iob_func' symbol
+				// (see https://golang.org/issue/23649 for details).
+				if p := ctxt.findLibPath("libmsvcrt.a"); p != "none" {
+					hostArchive(ctxt, p)
+				}
 				// TODO: maybe do something similar to peimporteddlls to collect all lib names
 				// and try link them all to final exe just like libmingwex.a and libmingw32.a:
 				/*

src/cmd/link/internal/loadpe/ldpe.go

@@ -445,11 +445,28 @@ func readpesym(arch *sys.Arch, syms *sym.Symbols, f *pe.File, pesym *pe.COFFSymb
 		name = sectsyms[f.Sections[pesym.SectionNumber-1]].Name
 	} else {
 		name = symname
+		switch arch.Family {
+		case sys.AMD64:
+			if name == "__imp___acrt_iob_func" {
+				// Do not rename __imp___acrt_iob_func into __acrt_iob_func,
+				// becasue __imp___acrt_iob_func symbol is real
+				// (see commit b295099 from git://git.code.sf.net/p/mingw-w64/mingw-w64 for detials).
+			} else {
 				name = strings.TrimPrefix(name, "__imp_") // __imp_Name => Name
-		if arch.Family == sys.I386 && name[0] == '_' {
+			}
+		case sys.I386:
+			if name == "__imp____acrt_iob_func" {
+				// Do not rename __imp____acrt_iob_func into ___acrt_iob_func,
+				// becasue __imp____acrt_iob_func symbol is real
+				// (see commit b295099 from git://git.code.sf.net/p/mingw-w64/mingw-w64 for detials).
+			} else {
+				name = strings.TrimPrefix(name, "__imp_") // __imp_Name => Name
+			}
+			if name[0] == '_' {
 				name = name[1:] // _Name => Name
 			}
 		}
+	}
 
 	// remove last @XXX
 	if i := strings.LastIndex(name, "@"); i >= 0 {