poco: fix m68k compile

Add a patch from double-conversion upstream project which is bundled
with poco to fix compile for m68k.

Fixes:
  http://autobuild.buildroot.net/results/791917c1343f53e12f27b06cfd5e1d2e88078014/
  http://autobuild.buildroot.net/results/349d4b49d65a652551c4de20233684bb4ffa5ae3/

Signed-off-by: Waldemar Brodkorb <wbx@openadk.org>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/poco/0002-fix-m68k-double-conv-detect.patch

@@ -0,0 +1,19 @@
+Fixes compile for m68k.
+
+From upstream double-conversion commit da111796231:
+https://github.com/google/double-conversion/blob/master/double-conversion/utils.h
+
+Signed-off-by: Waldemar Brodkorb <wbx@openadk.org>
+
+diff -Nur poco-poco-1.7.2-release.orig/Foundation/src/utils.h poco-poco-1.7.2-release/Foundation/src/utils.h
+--- poco-poco-1.7.2-release.orig/Foundation/src/utils.h	2016-03-19 08:19:35.000000000 +0100
++++ poco-poco-1.7.2-release/Foundation/src/utils.h	2016-08-11 02:55:02.827238119 +0200
+@@ -63,6 +63,8 @@
+     defined(__AARCH64EL__) || \
+     defined(nios2) || defined(__nios2) || defined(__nios2__)
+ #define DOUBLE_CONVERSION_CORRECT_DOUBLE_OPERATIONS 1
++#elif defined(__mc68000__)
++#undef DOUBLE_CONVERSION_CORRECT_DOUBLE_OPERATIONS
+ #elif defined(_M_IX86) || defined(__i386__) || defined(__i386)
+ #if defined(_WIN32)
+ // Windows uses a 64bit wide floating point stack.