disable backtrace for now. maybe possible to enable now that we have
libexecinfo in base, but needs checking to make sure we don't end up
with unresolved symbols.

Index: numpy/core/setup_common.py
--- numpy/core/setup_common.py.orig
+++ numpy/core/setup_common.py
@@ -131,7 +131,7 @@ OPTIONAL_STDFUNCS = ["expm1", "log1p", "acosh", "asinh
 
 OPTIONAL_LOCALE_FUNCS = ["strtold_l"]
 OPTIONAL_FILE_FUNCS = ["ftello", "fseeko", "fallocate"]
-OPTIONAL_MISC_FUNCS = ["backtrace", "madvise"]
+OPTIONAL_MISC_FUNCS = ["madvise"]
 
 
 OPTIONAL_HEADERS = [
