[AutoBuild] Throw error if using unsupported platforms with Julia v1.5- (#1020)

Author: giordano

src/AutoBuild.jl

@@ -123,6 +123,11 @@ function build_tarballs(ARGS, src_name, src_version, sources, script,
         return nothing
     end
 
+    # Throw an error if we're going to build for platforms not supported by Julia v1.5-.
+    if any(p -> arch(p) == "armv6l" || (Sys.isapple(p) && arch(p) == "aarch64"), platforms) && !occursin(r"1\.[67]", julia_compat)
+        error("Experimental platforms cannot be used with Julia v1.5-.\nChange `julia_compat` to require at least Julia v1.6")
+    end
+
     # XXX: These are needed as long as we support old-style sources and
     # dependencies.  Raise a warning for now, deprecate in BB 0.3+
     sources = coerce_source.(sources)

test/building.jl

@@ -293,6 +293,8 @@ end
             Dependency[],
         )
     end
+
+    @test_throws ErrorException build_tarballs(String[], "", v"1.0", GitSource[], "", supported_platforms(; experimental=true), LibraryProduct[], Dependency[])
 end
 
 @testset "AnyPlatform" begin