Use system perl or no-op on windows (#33)

Someone reported on Slack that MakieTeX doesn't work on windows, since Perl_jll doesn't build for the Windows platform. This PR works around that by using system Perl if it exists, or skipping it if it doesn't.

This currently executes on load but it may be worth it to execute on init instead, which would not be a difficult PR but would introduce some complications on how to handle this.

src/rendering.jl

@@ -5,6 +5,21 @@ function dvisvg()
     return DVISVGM_PATH[]
 end
 
+# Since perl_jll doesn't build for windows we check this.
+# todo define the function in a static block
+@static if Sys.iswindows() # !hasproperty(Perl_jll, :perl)
+        if isnothing(Sys.which("perl"))
+            @warn "Perl not found!  Skipping cropping step"
+            mtperl(f) = identity(f)
+        else
+            function mtperl(f)
+                    f(`perl`)
+            end
+        end
+else
+    mtperl(f) = Perl_jll.perl(f)
+end
+
 
 # The main compilation method - compiles arbitrary LaTeX documents
 function compile_latex(
@@ -90,7 +105,7 @@ function compile_latex(
                     redirect_stderr(devnull) do
                         redirect_stdout(devnull) do
                             Ghostscript_jll.gs() do gs_exe
-                                Perl_jll.perl() do perl_exe
+                                mtperl() do perl_exe
                                     run(`$perl_exe $pdfcrop --margin $crop_margins $() --gscmd $gs_exe temp.pdf temp_cropped.pdf`)
                                 end
                             end