scons: Add build_opts/ALL.

This enables all the ISAs, sets PROTOCOL to MI_example, and leaves
BUILD_GPU unset.

Change-Id: Id6243bb1b12fc70b8afee0aa213168ca421aff62

build_opts/ALL

diff --git a/build_opts/ALL b/build_opts/ALL
new file mode 100644
index 0000000..d7ce1fe
--- /dev/null
+++ b/build_opts/ALL
@@ -0,0 +1,7 @@
+USE_ARM_ISA = True
+USE_MIPS_ISA = True
+USE_POWER_ISA = True
+USE_RISCV_ISA = True
+USE_SPARC_ISA = True
+USE_X86_ISA = True
+PROTOCOL = 'MI_example'