Print more informative error when failing to hit build cache

This most often happens when there's something wrong with one of the
JLLs that constitute our toolchains, e.g. we try to deploy for a target
we haven't built yet.

Author: staticfloat

src/build_api/BuildConfig.jl

@@ -435,18 +435,22 @@ function build!(config::BuildConfig;
     # Hit our build cache and see if we've already done this exact build.
     if build_cache_enabled(meta) && !disable_cache && !isempty(extract_arg_hints)
         prepare(config; verbose)
-        build_hash = content_hash(config)
-        if all(haskey(meta.build_cache, build_hash, extract_content_hash(args...)) for args in extract_arg_hints)
-            if verbose
-                @info("Build cached", config, build_hash=content_hash(config))
-            end
-            try
-                result = BuildResult_cached(config)
-                meta.builds[config] = result
-                return result
-            catch exception
-                @error("Error while reading from build cache", exception=(exception, catch_backtrace()))
+        try
+            build_hash = content_hash(config)
+            if all(haskey(meta.build_cache, build_hash, extract_content_hash(args...)) for args in extract_arg_hints)
+                if verbose
+                    @info("Build cached", config, build_hash=content_hash(config))
+                end
+                try
+                    result = BuildResult_cached(config)
+                    meta.builds[config] = result
+                    return result
+                catch exception
+                    @error("Error while reading from build cache", exception=(exception, catch_backtrace()))
+                end
             end
+        catch e
+            @error("Unable to hit build cache", exception=(e, catch_backtrace()))
         end
     end