Fix the warnings when compiling harfbuzz with clang in Android

third_party/harfbuzz/contrib/harfbuzz-freetype.c

Index: third_party/harfbuzz/contrib/harfbuzz-freetype.c
diff --git a/third_party/harfbuzz/contrib/harfbuzz-freetype.c b/third_party/harfbuzz/contrib/harfbuzz-freetype.c
index a2962df48f60aa668c5b59668aff1ce690cd3a8f..f6a1e1ab141cb19333329ef1ebace2553715b9bd 100644
--- a/third_party/harfbuzz/contrib/harfbuzz-freetype.c
+++ b/third_party/harfbuzz/contrib/harfbuzz-freetype.c
@@ -21,7 +21,8 @@ hb_freetype_string_to_glyphs(HB_Font font,
   if (len > *numGlyphs)
     return 0;
 
-  size_t i = 0, j = 0;
+  ssize_t i = 0;
+  hb_uint32 j = 0;
   while (i < len) {
     const uint32_t cp = utf16_to_code_point(chars, len, &i);
     glyphs[j++] = FT_Get_Char_Index(face, cp);
@@ -53,7 +54,7 @@ static HB_Bool
 hb_freetype_can_render(HB_Font font, const HB_UChar16 *chars, hb_uint32 len) {
   FT_Face face = (FT_Face)font->userData;
 
-  size_t i = 0;
+  ssize_t i = 0;
   while (i < len) {
     const uint32_t cp = utf16_to_code_point(chars, len, &i);
     if (FT_Get_Char_Index(face, cp) == 0)