package.bbclass: Add '-b' option to file call in isELF

The isELF function works by running:

result = file <pathname>
if 'ELF' in result

By default 'file' will prepend the result with the path name of the file that is being checked. This usually works fine, such as:

$ file /home/foo/openembedded-core/meta/classes/package.bbclass
/home/foo/openembedded-core/meta/classes/package.bbclass: Python script, ASCII text executable, with very long lines

However, if the path includes 'ELF', ELF will end up in the result, and then the check will return positive.

$ file /home/ELF/openembedded-core/meta/classes/package.bbclass
/home/ELF/openembedded-core/meta/classes/package.bbclass: Python script, ASCII text executable, with very long lines

This will then result in the isELF coming back true, and possibly causing the checks that use isELF, such as the 'is it already stripped' check, to do the incorrect thing.

Adding the '-b' option to file will result in the path being omitted in the result:

$ file /home/ELF/openembedded-core/meta/classes/package.bbclass
Python script, ASCII text executable, with very long lines

---
 meta/classes/package.bbclass | 2 +-
 meta/lib/oe/package.py       | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

index 9bba021efb..79783071bc 100644
@@ -918,7 +918,7 @@ python split_and_strip_files () {
     # 16 - kernel module
     def isELF(path):
         type = 0
-        ret, result = oe.utils.getstatusoutput("file '%s'" % path)
+        ret, result = oe.utils.getstatusoutput("file -b '%s'" % path)
 
         if ret:
             msg = "split_and_strip_files: 'file %s' failed" % path

index 1e5c3aa8e1..599fca60f8 100644
@@ -73,7 +73,7 @@ def strip_execs(pn, dstdir, strip_cmd, libdir, base_libdir, qa_already_stripped=
     def is_elf(path):
         exec_type = 0
         ret, result = oe.utils.getstatusoutput(
-            "file \"%s\"" % path.replace("\"", "\\\""))
+            "file -b \"%s\"" % path.replace("\"", "\\\""))
 
         if ret:
             bb.error("split_and_strip_files: 'file %s' failed" % path)

2.16.0.rc2