libmakepkg/tidy: fix debug sources not being properly detected sometimes

DW_AT_comp_dir is meant to contain the directory in which the compiler
was run

DW_AT_name contains the source file the compiler was told to use.

In the event that DW_AT_name is an absolute path, it is (obviously) not
meant to be computed relative to DW_AT_comp_dir. However, we did not
handle this correctly, and as a result tried to copy source files using
doubled-up filepaths.

The correct approach should be to use DW_AT_name on its own, in the
event that it is an absolute path.

See http://wiki.dwarfstd.org/index.php?title=Best_Practices.

This fixes debug package generation for many packages that use absolute
paths in their build systems... like CMake.

Reported-by: Jagannathan Tiruvallur Eachambadi <jagannathante@gmail.com>
Signed-off-by: Eli Schwartz <eschwartz@archlinux.org>
Signed-off-by: Allan McRae <allan@archlinux.org>

scripts/libmakepkg/tidy/strip.sh.in

@@ -37,7 +37,7 @@ build_id() {
 
 source_files() {
 	LANG=C readelf "$1" --debug-dump | \
-		awk '/DW_AT_name +:/{name=$8}/DW_AT_comp_dir +:/{print $8 "/" name}'
+		awk '/DW_AT_name +:/{name=$8}/DW_AT_comp_dir +:/{{if (name !~ /^\//) {printf "%s/", $8}}{print name}}'
 }
 
 strip_file() {