configure: test for glibc backtrace even without glibc.
Other platform may have compatible facilities.
diff --git a/configure.ac b/configure.ac
index 63e8dcf..ad25012 100755
--- a/configure.ac
+++ b/configure.ac
@@ -1439,14 +1439,12 @@
dnl ---------------------------
dnl check for glibc 'backtrace'
dnl ---------------------------
-if test "${glibc}" = "yes"; then
- AC_CHECK_HEADER([execinfo.h],
- [AC_CHECK_FUNC([backtrace],
- [AC_DEFINE(HAVE_GLIBC_BACKTRACE,,[Glibc backtrace])
- AC_DEFINE(HAVE_STACK_TRACE,,[Stack symbol decoding])
- ])
- ])
-fi
+AC_CHECK_HEADER([execinfo.h],
+ [AC_CHECK_FUNC([backtrace],
+ [AC_DEFINE(HAVE_GLIBC_BACKTRACE,,[Glibc backtrace])
+ AC_DEFINE(HAVE_STACK_TRACE,,[Stack symbol decoding])
+ ])
+])
dnl -----------------------------------------
dnl check for malloc mallinfo struct and call