build: unbreak __get_osslibdir__()

- without Utils.* always returns empty string
- subprocess doesn't need extra quoting for sh -c
- "source" is a bash'ism, not in POSIX sh
- most shell commands embed newline at the end

waftools/checks/custom.py

@@ -76,12 +76,14 @@ def __fail_oss_check__(ctx):
     return False
 
 def __get_osslibdir__():
+    from waflib import Utils
+
     try:
-        cmd = ['sh', '-c', "'source /etc/oss.conf && echo $OSSLIBDIR'"]
+        cmd = ['sh', '-c', '. /etc/oss.conf && echo $OSSLIBDIR']
         p = Utils.subprocess.Popen(cmd, stdin=Utils.subprocess.PIPE,
                                         stdout=Utils.subprocess.PIPE,
                                         stderr=Utils.subprocess.PIPE)
-        return p.communicate()[0]
+        return p.communicate()[0].rstrip()
     except Exception:
         return ""