nixpkgs/pkgs/applications/blockchains/fix-bitcoin-qt-build.patch

--- bitcoin-abc-v0.15.0-src/build-aux/m4/bitcoin_qt.m4	1970-01-01 01:00:01.000000000 +0100
+++ bitcoin-abc-v0.15.0-src.org/build-aux/m4/bitcoin_qt.m4	2017-09-27 23:38:44.748384197 +0100
@@ -35,11 +35,7 @@
 dnl Output: $1 is set to the path of $2 if found. $2 are searched in order.
 AC_DEFUN([BITCOIN_QT_PATH_PROGS],[
   BITCOIN_QT_CHECK([
-    if test "x$3" != x; then
-      AC_PATH_PROGS($1,$2,,$3)
-    else
-      AC_PATH_PROGS($1,$2)
-    fi
+    AC_PATH_PROGS($1,$2)
     if test "x$$1" = x && test "x$4" != xyes; then
       BITCOIN_QT_FAIL([$1 not found])
     fi