[RFAv2] Fix leak due to assigning a xstrdup-ed string to the std::string gdb_datadir

[Philippe Waroquiers <philippe.waroquiers@skynet.be>]

Valgrind reports the following leak:
==32623== 56 bytes in 1 blocks are definitely lost in loss record 1,099 of 6,654
==32623==    at 0x4835753: malloc (vg_replace_malloc.c:307)
==32623==    by 0x25CF67: xmalloc (alloc.c:60)
==32623==    by 0x65FBD9: xstrdup (xstrdup.c:34)
==32623==    by 0x413D9E: captured_main_1(captured_main_args*) (main.c:553)
==32623==    by 0x414FFA: captured_main (main.c:1172)
==32623==    by 0x414FFA: gdb_main(captured_main_args*) (main.c:1197)
==32623==    by 0x22531A: main (gdb.c:32)

Commit f2aec7f6d14 changed gdb_datadir to std::string.
So, xstrdup-ing the result of relocate_gdb_directory (returning a std::string)
is not needed and creates a leak.

Fix the leak by removing the xstrdup and the not needed c_str ().
Also removes a useless conversion of gdb_datadir to std::string.

gdb/ChangeLog
YYYY-MM-DD  Philippe Waroquiers  <philippe.waroquiers@skynet.be>

	* main.c (relocate_gdbinit_path_maybe_in_datadir): Remove std::string
	conversion of gdb_datadir.
	(captured_main_1): Remove xstrdup when assigning to gdb_datadir,
	remove not needed c_str ().
---
 gdb/main.c | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/gdb/main.c b/gdb/main.c
index 7fab8ff8da..14d9e79653 100644
--- a/gdb/main.c
+++ b/gdb/main.c
@@ -214,8 +214,7 @@ relocate_gdbinit_path_maybe_in_datadir (const std::string& file)
       size_t start = datadir_len;
       for (; IS_DIR_SEPARATOR (file[start]); ++start)
 	;
-      relocated_path = (std::string (gdb_datadir) + SLASH_STRING
-			+ file.substr (start));
+      relocated_path = gdb_datadir + SLASH_STRING + file.substr (start);
     }
   else
     {
@@ -549,9 +548,8 @@ captured_main_1 (struct captured_main_args *context)
     = xstrdup (relocate_gdb_directory (DEBUGDIR,
 				     DEBUGDIR_RELOCATABLE).c_str ());
 
-  gdb_datadir
-    = xstrdup (relocate_gdb_directory (GDB_DATADIR,
-				     GDB_DATADIR_RELOCATABLE).c_str ());
+  gdb_datadir = relocate_gdb_directory (GDB_DATADIR,
+					GDB_DATADIR_RELOCATABLE);
 
 #ifdef WITH_PYTHON_PATH
   {
-- 
2.20.1