[process][posix] use os.Lstat for symlink check

unix.DT_LNK is not portable; per glibc docs it's a BSD extension. It is
not available e.g. in Solaris.
https://www.gnu.org/software/libc/manual/html_node/Directory-Entries.html#index-DT_005fLNK

As a side effect, fixes incorrect equality comparison against
Stat_t.Mode, a bitmask.

process/process_posix.go

@@ -75,11 +75,16 @@ func getTerminalMap() (map[uint64]string, error) {
 // https://github.com/python/cpython/blob/08ff4369afca84587b1c82034af4e9f64caddbf2/Lib/posixpath.py#L186-L216
 // https://docs.python.org/3/library/os.path.html#os.path.ismount
 func isMount(path string) bool {
-	var stat1 unix.Stat_t
-	if err := unix.Lstat(path, &stat1); err != nil {
+	// Check symlinkness with os.Lstat; unix.DT_LNK is not portable
+	fileInfo, err := os.Lstat(path)
+	if err != nil {
+		return false
+	}
+	if fileInfo.Mode() & os.ModeSymlink != 0 {
 		return false
 	}
-	if stat1.Mode == unix.DT_LNK {
+	var stat1 unix.Stat_t
+	if err := unix.Lstat(path, &stat1); err != nil {
 		return false
 	}
 	parent := filepath.Join(path, "..")
@@ -98,6 +103,7 @@ func PidExistsWithContext(ctx context.Context, pid int32) (bool, error) {
 	if err != nil {
 		return false, err
 	}
+
 	if isMount(common.HostProc()) { // if /<HOST_PROC>/proc exists and is mounted, check if /<HOST_PROC>/proc/<PID> folder exists
 		_, err := os.Stat(common.HostProc(strconv.Itoa(int(pid))))
 		if os.IsNotExist(err) {

v3/process/process_posix.go

@@ -75,11 +75,16 @@ func getTerminalMap() (map[uint64]string, error) {
 // https://github.com/python/cpython/blob/08ff4369afca84587b1c82034af4e9f64caddbf2/Lib/posixpath.py#L186-L216
 // https://docs.python.org/3/library/os.path.html#os.path.ismount
 func isMount(path string) bool {
-	var stat1 unix.Stat_t
-	if err := unix.Lstat(path, &stat1); err != nil {
+	// Check symlinkness with os.Lstat; unix.DT_LNK is not portable
+	fileInfo, err := os.Lstat(path)
+	if err != nil {
 		return false
 	}
-	if stat1.Mode == unix.DT_LNK {
+	if fileInfo.Mode() & os.ModeSymlink != 0 {
+		return false
+	}
+	var stat1 unix.Stat_t
+	if err := unix.Lstat(path, &stat1); err != nil {
 		return false
 	}
 	parent := filepath.Join(path, "..")