apr: add configure vars and caches

apr's configure script uses lots of AC_TRY_RUNs and when cross-compiling
needs a leg-up. This commit adds more configure variables (and removes
one, too).

Notable changes:

 - apr_cv_use_lfs64=yes is removed (again) after having a discussion
   about it with the musl developers. The conclusion was that
   _LARGEFILE64_SOURCE is a horrible thing that we don't want and should
   avoid (hence the removal of the variable, because defining
   _LARGEFILE64_SOURCE is all it does).
 - ap_cv_atomic_builtins is set to "yes" for 64-bit platforms. If
   anybody is interested in enabling this for other targets feel free to
   send a patch after testing it.
 - configure doesn't add -lpthread to LIBS when cross-compiling. This is
   not a problem for musl but might be for other libcs. This commit adds
   to related variable.
 - configure caches are added (via patches) for strerror and /dev/zero
   mmap tests. The former fixes a warning on musl (where strerror
   returns int instead of a pointer) and the latter is required for
   pthread pshared mutex apr_lock implementation and cannot be detected
   during cross-compile either.

Signed-off-by: Sebastian Kemper <sebastian_ml@gmx.net>

libs/apr/patches/302-add-cache-for-strerror_r.patch

@@ -0,0 +1,30 @@
+--- a/build/apr_common.m4
++++ b/build/apr_common.m4
+@@ -526,8 +526,9 @@ dnl  string.
+ dnl
+ dnl
+ AC_DEFUN([APR_CHECK_STRERROR_R_RC], [
+-AC_MSG_CHECKING(for type of return code from strerror_r)
+-AC_TRY_RUN([
++AC_CACHE_CHECK([whether return code from strerror_r has type int],
++[ac_cv_strerror_r_rc_int],
++[AC_TRY_RUN([
+ #include <errno.h>
+ #include <string.h>
+ #include <stdio.h>
+@@ -543,14 +544,10 @@ main()
+ }], [
+     ac_cv_strerror_r_rc_int=yes ], [
+     ac_cv_strerror_r_rc_int=no ], [
+-    ac_cv_strerror_r_rc_int=no ] )
++    ac_cv_strerror_r_rc_int=no ] ) ] )
+ if test "x$ac_cv_strerror_r_rc_int" = xyes; then
+   AC_DEFINE(STRERROR_R_RC_INT, 1, [Define if strerror returns int])
+-  msg="int"
+-else
+-  msg="pointer"
+ fi
+-AC_MSG_RESULT([$msg])
+ ] )
+ 
+ dnl