README: Fix/improve Ubuntu/Fedora build instructions

The current instructions for Ubuntu/Fedora are missing a couple of dependencies
and in the Ubuntu case the CROSS= prefix doesn't match the compiler package name.

Add missing xz and make dependencies. Recommend the use of a powerpc64le
bi-endian toolchain, and change dependencies and CROSS= variables to match that.

Fixes: 8fbf67e5b1bd ("README: Update build instructions")
Reported-by: Mark Linimon <linimon@freebsd.org>
Suggested-by: Jeremy Kerr <jk@ozlabs.org>
Signed-off-by: Andrew Donnellan <andrew.donnellan@au1.ibm.com>
Signed-off-by: Stewart Smith <stewart@linux.vnet.ibm.com>

1 files changed, 10 insertions, 5 deletions

diff --git a/README.md b/README.md
index 7042b8e4..5a0742b0 100644
--- a/README.md
+++ b/README.md
@@ -53,17 +53,22 @@ package management tools.
 To build on Ubuntu:
 ```
 apt-get install gcc-powerpc64le-linux-gnu gcc valgrind \
-	expect libssl-dev device-tree-compiler
-CROSS=powerpc64-linux-gnu- make -j`nproc`
+	expect libssl-dev device-tree-compiler make \
+	xz-utils
+CROSS=powerpc64le-linux-gnu- make -j`nproc`
 ```
 
 To build on Fedora:
 ```
-dnf install gcc-powerpc64-linux-gnu binutils-powerpc64-linux-gnu gcc make \
-    diffutils findutils expect valgrind-devel dtc openssl-devel
-CROSS=powerpc64-linux-gnu- make -j`nproc`
+dnf install gcc-powerpc64le-linux-gnu binutils-powerpc64-linux-gnu gcc make \
+    diffutils findutils expect valgrind-devel dtc openssl-devel xz
+CROSS=powerpc64le-linux-gnu- make -j`nproc`
 ```
 
+(The little-endian powerpc64le compilers in Ubuntu and Fedora are actually
+bi-endian and can compile skiboot even though it's big-endian. We recommend
+installing a little-endian toolchain if you plan on building other projects.)
+
 On any POWER system with a bi-endian system compiler:
 ```
 CROSS="" make -j`nproc`