Move gdb_regex to gdbsupport

This moves the gdb_regex convenience class to gdbsupport.

gdbsupport/gdb_regex.h

@@ -0,0 +1,57 @@
+/* Portable <regex.h>.
+   Copyright (C) 2000-2022 Free Software Foundation, Inc.
+
+   This file is part of GDB.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+#ifndef GDB_REGEX_H
+#define GDB_REGEX_H 1
+
+# include "xregex.h"
+
+/* A compiled regex.  This is mainly a wrapper around regex_t.  The
+   the constructor throws on regcomp error and the destructor is
+   responsible for calling regfree.  The former means that it's not
+   possible to create an instance of compiled_regex that isn't
+   compiled, hence the name.  */
+class compiled_regex
+{
+public:
+  /* Compile a regexp and throw an exception on error, including
+     MESSAGE.  REGEX and MESSAGE must not be NULL.  */
+  compiled_regex (const char *regex, int cflags,
+		  const char *message)
+    ATTRIBUTE_NONNULL (2) ATTRIBUTE_NONNULL (4);
+
+  ~compiled_regex ();
+
+  DISABLE_COPY_AND_ASSIGN (compiled_regex);
+
+  /* Wrapper around ::regexec.  */
+  int exec (const char *string,
+	    size_t nmatch, regmatch_t pmatch[],
+	    int eflags) const;
+
+  /* Wrapper around ::re_search.  (Not const because re_search's
+     regex_t parameter isn't either.)  */
+  int search (const char *string, int size, int startpos,
+	      int range, struct re_registers *regs);
+
+private:
+  /* The compiled pattern.  */
+  regex_t m_pattern;
+};
+
+#endif /* not GDB_REGEX_H */