Update README.arm.md based on recent improvements.

[ci skip]

README.arm.md

@@ -5,11 +5,12 @@ Chromebooks running Ubuntu Linux under Crouton, Raspberry Pi systems
 and Odroid boards. This is a work in progress - several tests are
 known to fail, and backtraces are not available.
 
-Most of the build failures in building the Julia system image are due
-to LLVM not being able to detect the correct ARM processor type and
-features. Experimenting with different `JULIA_CPU_ARCH` settings can
-help in such cases. For example, this is needed on Raspberry Pi, as
-discussed below.
+Julia on ARM can be built by simply typing `make`, which will download all
+the relevant libraries. This is the *recommended* way, and it will take a
+few hours.
+
+If you get SIGILL during sysimg.o creation, it is likely that your cpu does not support VFP.
+File an issue on the Julia issue tracker with the contents of /proc/cpuinfo.
 
 This is the list of known issues on ARM:
  [https://github.com/JuliaLang/julia/labels/arm](https://github.com/JuliaLang/julia/labels/arm)
@@ -19,19 +20,7 @@ This is the list of known issues on ARM:
 We recommend using at least Ubuntu 14.04 and gcc 4.8, which is part of the
 standard `build-essentials`.
 
-Julia on ARM can be built by simply typing `make`, which will download all
-the relevant libraries. This is the *recommended* way, and it will take a
-few hours.
-
-OpenBLAS detects the target architecture reasonably well, but in case
-it does not, you can force the target architecture should you need to in
-`Make.user`.
-
-````
-override OPENBLAS_TARGET_ARCH=ARMV7
-````
-
-Similarly, one can install other system libraries instead of building them,
+One can install other system libraries instead of building them,
 should the build be troublesome, by adding the following lines in `Make.user`:
 
 ````
@@ -50,6 +39,9 @@ The following command will install all the necessary libraries on Ubuntu.
 sudo apt-get install libblas3gf liblapack3gf libfftw3-dev libgmp3-dev libmpfr-dev libblas-dev liblapack-dev cmake gcc-4.8 g++-4.8 gfortran libgfortran3 m4 libedit-dev
 ````
 
+Note that OpenBLAS only supports ARMv7. For older ARM variants, using the reference BLAS
+may be the simplest thing to do.
+
 # ARM specific build problems
 
 If you run into issues building LLVM, see these notes:
@@ -58,12 +50,12 @@ If you run into issues building LLVM, see these notes:
 # Raspberry Pi
 
 The Raspberry Pi ARM CPU type is not detected by LLVM.
-Before starting the build, it is recommented to add `export JULIA_CPU_ARCH=arm1176jzf-s`
-to your Make.user file to tune the generated code for your CPU architecture.
+Before starting the build, it is recommended to do `export JULIA_CPU_ARCH=arm1176jzf-s`
+at the shell to tune the generated code for your CPU architecture.
 
 # Raspberry Pi 2
 
-In the case of Raspberry Pi 2, download LLVM binaries from the LLVM website, since building LLVM on our own for some reason does not produce a working build.
+In the case of Raspberry Pi 2, in case the default build fails, download LLVM binaries from the LLVM website.
 
 1. Download the [LLVM 3.6.1 binaries for ARMv7a] (http:https://llvm.org/releases/3.6.1/clang+llvm-3.6.1-armv7a-linux-gnueabihf.tar.xz) and extract them in a local directory.
 2. For each file in the extracted `bin`, `include`, and `lib` subdirectories, create symlinks from the corresponding directory under `/usr/local`.
@@ -72,11 +64,6 @@ In the case of Raspberry Pi 2, download LLVM binaries from the LLVM website, sin
 override USE_SYSTEM_LLVM=1
 ```
 
-# SIGILL during sysimg.o creation
-
-Its likely that your cpu does not support VFP. File an issue on the Julia issue tracker with the contents of /proc/cpuinfo.
-
-
 # Chromebook
 
 On Chromebooks, you have to first install Crouton. If you do not have