misc/silicon: fix build on ARM / POWER

error[E0308]: mismatched types
   --> src/hb_wrapper.rs:17:17
    |
16  |             hb_feature_from_string(
    |             ---------------------- arguments to this function are incorrect
17  |                 tag.as_ptr() as *const i8,
    |                 ^^^^^^^^^^^^^^^^^^^^^^^^^ expected `u8`, found `i8`
    |
    = note: expected raw pointer `*const u8`
               found raw pointer `*const i8`

misc/silicon/files/patch-src_hb__wrapper.rs

@@ -0,0 +1,28 @@
+--- src/hb_wrapper.rs.orig	2023-04-25 09:08:05 UTC
++++ src/hb_wrapper.rs
+@@ -6,6 +6,7 @@ use font_kit::loaders::freetype::NativeFont;
+ // use harfbuzz for shaping ligatures
+ pub use harfbuzz::*;
+ use harfbuzz_sys as harfbuzz;
++use std::os::raw::c_char;
+ use std::mem;
+
+ /// font feature tag
+@@ -14,7 +15,7 @@ pub fn feature_from_tag(tag: &str) -> Result<hb_featur
+         let mut feature = mem::zeroed();
+         ensure!(
+             hb_feature_from_string(
+-                tag.as_ptr() as *const i8,
++                tag.as_ptr() as *const c_char,
+                 tag.len() as i32,
+                 &mut feature as *mut _
+             ) != 0,
+@@ -88,7 +89,7 @@ impl HBBuffer {
+         unsafe {
+             hb_buffer_add_utf8(
+                 self.buffer,
+-                s.as_ptr() as *const i8,
++                s.as_ptr() as *const c_char,
+                 s.len() as i32,
+                 0,
+                 s.len() as i32,