produce stripped bin output on demand

a resonably good output is now produced with the following:

    zig build -Drelease-safe -Dstrip

build.zig

@@ -3,6 +3,10 @@ const std = @import("std");
 pub fn build(b: *std.build.Builder) void {
     const target = b.standardTargetOptions(.{});
     const mode = b.standardReleaseOptions();
+    const do_strip = b.option(bool, "strip", "Strip final output; on for release-small") orelse switch (mode) {
+        .ReleaseSmall => true,
+        else => false,
+    };
 
     const libsegfault = b.addStaticLibrary("segfault", "src/segfault.zig");
     libsegfault.setTarget(target);
@@ -12,6 +16,7 @@ pub fn build(b: *std.build.Builder) void {
     const exe = b.addExecutable("st", null);
     exe.setTarget(target);
     exe.setBuildMode(mode);
+    exe.strip = do_strip;
     exe.install();
     exe.linkLibrary(libsegfault);
     exe.linkSystemLibrary("fontconfig");