Add libiberty/concat styled concat_path function

This commit adds concat_path function to concatenate an arbitrary number of
    path elements.  The function automatically adds an directory separator between
    two elements as needed.

    gdb/ChangeLog:

	* common/common-utils.h (endswith): New function.
	* utils.c (_concat_path, approx_path_length): New function.
	* utils.h (_concat_path): New export.
	(concat_path): New define.

gdb/common/common-utils.h

@@ -83,6 +83,17 @@ startswith (const char *string, const char *pattern)
   return strncmp (string, pattern, strlen (pattern)) == 0;
 }
 
+/* Return non-zero if the end of STRING matches PATTERN, zero
+   otherwise.  */
+
+static inline int
+endswith (const char *string, const char *pattern)
+{
+  return (strlen (string) > strlen (pattern)
+	  && strncmp (string + strlen (string) - strlen (pattern), pattern,
+		      strlen (pattern)) == 0);
+}
+
 ULONGEST strtoulst (const char *num, const char **trailer, int base);
 
 /* Skip leading whitespace characters in INP, returning an updated

gdb/utils.c

@@ -3181,6 +3181,52 @@ substitute_path_component (std::string &str, const std::string &from,
     }
 }
 
+/* Approximate length of final path.  Helper for concat_path.  */
+
+static inline unsigned long
+approx_path_length (std::initializer_list<std::string> args,
+		   std::string dir_separator)
+{
+  size_t length = 0;
+
+  for (const std::string &arg: args)
+      length += arg.length () + dir_separator.length ();
+
+  return length;
+}
+
+/* See utils.h.  */
+
+std::string
+_concat_path (std::initializer_list<std::string> args,
+	      std::string dir_separator)
+{
+  std::string dst;
+  dst.reserve (approx_path_length (args, dir_separator));
+
+  for (const std::string &arg : args)
+    {
+      if (arg.empty ())
+	continue;
+
+      if (startswith (arg.c_str (), dir_separator.c_str ())
+	  && endswith (dst.c_str (), dir_separator.c_str ()))
+	dst.erase (dst.length () - dir_separator.length (),
+		   dir_separator.length ());
+
+      else if (!dst.empty ()
+	       && !startswith (arg.c_str (), dir_separator.c_str ())
+	       && !endswith (dst.c_str (), dir_separator.c_str ())
+	       && dst != TARGET_SYSROOT_PREFIX)
+	dst += dir_separator;
+
+      dst += arg;
+    }
+
+  dst.shrink_to_fit ();
+  return dst;
+}
+
 #ifdef HAVE_WAITPID
 
 #ifdef SIGALRM

gdb/utils.h

@@ -24,6 +24,7 @@
 #include "exceptions.h"
 #include "common/scoped_restore.h"
 #include <chrono>
+#include <string>
 
 extern void initialize_utils (void);
 
@@ -140,6 +141,22 @@ extern void substitute_path_component (std::string &str,
 				       const std::string &from,
 				       const std::string &to);
 
+/* Concatenate an arbitrary number of path elements.  Adds and removes
+   directory separators as needed.
+
+   concat_path (/first, second)		=> /first/second
+   concat_path (first, second)		=> first/second
+   concat_path (first/, second)		=> first/second
+   concat_path (first, /second)		=> first/second
+   concat_path (first/, /second)	=> first/second
+   concat_path (target:, second)	=> target:second
+   */
+
+extern std::string _concat_path (std::initializer_list<std::string> args,
+				 std::string dir_separator);
+
+#define concat_path(...) _concat_path ({__VA_ARGS__}, SLASH_STRING)
+
 char *ldirname (const char *filename);
 
 extern int count_path_elements (const char *path);