[binutils] Handle absolute DW_AT_dwo_name

With an exec:
...
$ pwd
/home/vries/tmp
$ gcc /home/vries/tmp/src/hello.c -gsplit-dwarf -c \
  -o /home/vries/tmp/obj/hello.o
...
I get:
...
$ readelf -w obj/hello.o > READELF
readelf: Warning: Unable to load dwo file: \
  /home/vries/tmp//home/vries/tmp/obj/hello.dwo
...

The dwo file name is listed here:
...
    <20>   DW_AT_GNU_dwo_name: /home/vries/tmp/obj/hello.dwo
    <24>   DW_AT_comp_dir    : /home/vries/tmp
...

The standard states about the DW_AT_dwo_name attribute:
...
value is a null-terminated string containing the full or relative path name
(relative to the value of the DW_AT_comp_dir attribute, see below) of the
object file that contains the full compilation unit.
...

So, readelf shouldn't try to prefix an absolute path with DW_AT_comp_dir.

Fix this in load_dwo_file by handling the absolute path case.

binutils/ChangeLog:

2021-02-10  Tom de Vries  <tdevries@suse.de>

	PR binutils/27391
	* dwarf.c (load_dwo_file): Handle case that name is absolute path.

1 files changed, 5 insertions, 2 deletions

diff --git a/binutils/dwarf.c b/binutils/dwarf.c
index 84d63f6..3cbd197 100644
--- a/binutils/dwarf.c
+++ b/binutils/dwarf.c
@@ -11092,8 +11092,11 @@ load_dwo_file (const char * main_filename, const char * name, const char * dir,
   char * separate_filename;
   void * separate_handle;
 
-  /* FIXME: Skip adding / if dwo_dir ends in /.  */
-  separate_filename = concat (dir, "/", name, NULL);
+  if (IS_ABSOLUTE_PATH (name))
+    separate_filename = strdup (name);
+  else
+    /* FIXME: Skip adding / if dwo_dir ends in /.  */
+    separate_filename = concat (dir, "/", name, NULL);
   if (separate_filename == NULL)
     {
       warn (_("Out of memory allocating dwo filename\n"));