add missing multibyte/internal.c in musl
diff --git a/tools/shared.py b/tools/shared.py
index 9873549..764877b 100644
--- a/tools/shared.py
+++ b/tools/shared.py
@@ -345,7 +345,7 @@
 # we re-check sanity when the settings are changed)
 # We also re-check sanity and clear the cache when the version changes
 
-EMSCRIPTEN_VERSION = '1.10.3'
+EMSCRIPTEN_VERSION = '1.10.4'
 
 def generate_sanity():
   return EMSCRIPTEN_VERSION + '|' + get_llvm_target() + '|' + LLVM_ROOT + '|' + get_clang_version()
diff --git a/tools/system_libs.py b/tools/system_libs.py
index 92f0e24..3723a5c 100644
--- a/tools/system_libs.py
+++ b/tools/system_libs.py
@@ -187,6 +187,7 @@
        ]],
        ['multibyte', [
         'btowc.c',
+        'internal.c',
         'mblen.c',
         'mbrlen.c',
         'mbrtowc.c',