buildroot: update to 2018.05

Verify that OpenBLAS x86 build is working as mentioned at:
https://bugs.busybox.net/show_bug.cgi?id=10856#c1

README.adoc

@@ -5645,24 +5645,12 @@ Source: link:kernel_module/user/openmp.c[]
 Buildroot supports it, which makes everything just trivial:
 
 ....
-./build -a arm -B 'BR2_PACKAGE_OPENBLAS=y' -k
+./build -B 'BR2_PACKAGE_OPENBLAS=y' -k
 ./run -F '/openblas.out'
 ....
 
 Source: link:kernel_module/user/openblas.c[]
 
-For x86, you also need:
-
-....
--B 'BR2_PACKAGE_OPENBLAS_TARGET="NEHALEM"'
-....
-
-to overcome this bug: https://bugs.busybox.net/show_bug.cgi?id=10856
-
-....
-sgemm_kernel.o: No such file or directory
-....
-
 ===== Eigen
 
 Header only linear algebra library supported by Buildroot:

kernel_module/user/openblas.c

@@ -1,7 +1,4 @@
-/*
-OpenBLAS hello world, initially adapted from:
-https://stackoverflow.com/questions/49227682/gem5-can-not-simulate-my-program-that-calls-openblas-functions-with-an-fatal-err
-*/
+/* Adapted from: https://github.com/xianyi/OpenBLAS/wiki/User-Manual/59b62f98e7400270fb03ad1d85fba5b64ebbff2b#call-cblas-interface */
 
 #include <cblas.h>
 #include <stdio.h>