go/build: recognize '.sx' as equivalent of '.S'

On case insensitive filesystems, '.S' is interpreted as '.s' so,
providing option to use '.sx' extension for '.S' files as an alternative.

Fixes #32434

Change-Id: Ie2f7e5e2f3f12690ce18659e30ca94252a8f7bfc
GitHub-Last-Rev: dcca989ec41ddc1d06ea509b78dce7d70bc996ed
GitHub-Pull-Request: golang/go#32557
Reviewed-on: https://go-review.googlesource.com/c/go/+/181699
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/cmd/cgo/doc.go

@@ -99,7 +99,7 @@ Will be expanded to:
 
 When the Go tool sees that one or more Go files use the special import
 "C", it will look for other non-Go files in the directory and compile
-them as part of the Go package. Any .c, .s, or .S files will be
+them as part of the Go package. Any .c, .s, .S or .sx files will be
 compiled with the C compiler. Any .cc, .cpp, or .cxx files will be
 compiled with the C++ compiler. Any .f, .F, .for or .f90 files will be
 compiled with the fortran compiler. Any .h, .hh, .hpp, or .hxx files will

src/cmd/go/alldocs.go

@@ -1510,8 +1510,8 @@
 // extension will be passed to SWIG. Any file with a .swigcxx extension
 // will be passed to SWIG with the -c++ option.
 //
-// When either cgo or SWIG is used, go build will pass any .c, .m, .s,
-// or .S files to the C compiler, and any .cc, .cpp, .cxx files to the C++
+// When either cgo or SWIG is used, go build will pass any .c, .m, .s, .S
+// or .sx files to the C compiler, and any .cc, .cpp, .cxx files to the C++
 // compiler. The CC or CXX environment variables may be set to determine
 // the C or C++ compiler, respectively, to use.
 //
@@ -1730,7 +1730,7 @@
 // 	.m
 // 		Objective-C source files. Only useful with cgo, and always
 // 		compiled with the OS-native compiler.
-// 	.s, .S
+// 	.s, .S, .sx
 // 		Assembler source files.
 // 		If the package uses cgo or SWIG, these will be assembled with the
 // 		OS-native assembler (typically gcc (sic)); otherwise they

src/cmd/go/internal/help/helpdoc.go

@@ -21,8 +21,8 @@ http://swig.org/. When running go build, any file with a .swig
 extension will be passed to SWIG. Any file with a .swigcxx extension
 will be passed to SWIG with the -c++ option.
 
-When either cgo or SWIG is used, go build will pass any .c, .m, .s,
-or .S files to the C compiler, and any .cc, .cpp, .cxx files to the C++
+When either cgo or SWIG is used, go build will pass any .c, .m, .s, .S
+or .sx files to the C compiler, and any .cc, .cpp, .cxx files to the C++
 compiler. The CC or CXX environment variables may be set to determine
 the C or C++ compiler, respectively, to use.
 	`,
@@ -645,7 +645,7 @@ the extension of the file name. These extensions are:
 	.m
 		Objective-C source files. Only useful with cgo, and always
 		compiled with the OS-native compiler.
-	.s, .S
+	.s, .S, .sx
 		Assembler source files.
 		If the package uses cgo or SWIG, these will be assembled with the
 		OS-native assembler (typically gcc (sic)); otherwise they

src/go/build/build.go

@@ -773,7 +773,7 @@ Found:
 	}
 
 	var badGoError error
-	var Sfiles []string // files with ".S" (capital S)
+	var Sfiles []string // files with ".S"(capital S)/.sx(capital s equivalent for case insensitive filesystems)
 	var firstFile, firstCommentFile string
 	imported := make(map[string][]token.Position)
 	testImported := make(map[string][]token.Position)
@@ -827,7 +827,7 @@ Found:
 		case ".s":
 			p.SFiles = append(p.SFiles, name)
 			continue
-		case ".S":
+		case ".S", ".sx":
 			Sfiles = append(Sfiles, name)
 			continue
 		case ".swig":
@@ -967,7 +967,7 @@ Found:
 	p.TestImports, p.TestImportPos = cleanImports(testImported)
 	p.XTestImports, p.XTestImportPos = cleanImports(xTestImported)
 
-	// add the .S files only if we are using cgo
+	// add the .S/.sx files only if we are using cgo
 	// (which means gcc will compile them).
 	// The standard assemblers expect .s files.
 	if len(p.CgoFiles) > 0 {
@@ -1274,7 +1274,7 @@ func (ctxt *Context) matchFile(dir, name string, allTags map[string]bool, binary
 	}
 
 	switch ext {
-	case ".go", ".c", ".cc", ".cxx", ".cpp", ".m", ".s", ".h", ".hh", ".hpp", ".hxx", ".f", ".F", ".f90", ".S", ".swig", ".swigcxx":
+	case ".go", ".c", ".cc", ".cxx", ".cpp", ".m", ".s", ".h", ".hh", ".hpp", ".hxx", ".f", ".F", ".f90", ".S", ".sx", ".swig", ".swigcxx":
 		// tentatively okay - read to make sure
 	case ".syso":
 		// binary, no reading