Allow prjconf to disable the building of the armv7/aarch64 builds.

The prjconf can override the "enabled by default" values by setting
rust_disable_armv7 and/or rust_disable_aarch64 to 1.

Signed-off-by: David Greaves <david.greaves@jolla.com>

Author: lbt

rust.spec

@@ -32,13 +32,25 @@
 %endif
 %endif
 
+# The prjconf can override the "enabled by default" by setting
+# rust_disable_armv7 to 1
+%define build_armv7 %{?rust_disable_armv7:0}%{!?rust_disable_armv7:1}
+%define build_aarch64 %{?rust_disable_aarch64:0}%{!?rust_disable_aarch64:1}
+
+%if 0%{?build_armv7}
 %global rust_arm_triple armv7-unknown-linux-gnueabihf
+%define rust_arm_triple_comma ,%{rust_arm_triple}
+%else
+%define rust_arm_triple_comma ""
+%endif
+%if 0%{?build_aarch64}
 %global rust_aarch64_triple aarch64-unknown-linux-gnu
+%define rust_aarch64_triple_comma ,%{rust_aarch64_triple}
+%else
+%define rust_aarch64_triple_comma ""
+%endif
 %global rust_x86_triple i686-unknown-linux-gnu
 
-%define build_armv7 1
-%define build_aarch64 1
-
 %global python python3
 
 # LLDB isn't available everywhere...
@@ -296,11 +308,7 @@ PATH=/opt/cross/bin/:$PATH
  --disable-option-checking \
   --libdir=%{common_libdir} \
   --build=%{rust_x86_triple} --host=%{rust_x86_triple}\
-%if 0%{?build_aarch64}
-  --target=%{rust_x86_triple},%{rust_arm_triple}\,%{rust_aarch64_triple}\
-%else
-  --target=%{rust_x86_triple},%{rust_arm_triple}\
-%endif
+  --target=%{rust_x86_triple}%{rust_arm_triple_comma}%{rust_aarch64_triple_comma}\
   --python=%{python} \
   --local-rust-root=%{local_rust_root} \
   --enable-local-rebuild \