Musl: set use_glib = false

This fixes the following errors:

    ld: cannot find -lglib-2.0
    ld: cannot find -lgmodule-2.0
    ld: cannot find -lgobject-2.0
    ld: cannot find -lgthread-2.0

These errors appeared after the introduction of `CPDF_FontSubsetter` in the following commit:
https://pdfium.googlesource.com/pdfium/+/4f046db1f31d7bb2e53ab7dd12e48b837ac568be

Author: bblanchon

steps/05-configure.sh

@@ -73,6 +73,7 @@ mkdir -p "$BUILD"
       echo 'is_clang = false'
       echo 'use_custom_libcxx = false'
       echo 'use_custom_libcxx_for_host = false'
+      echo 'use_glib = false'
       [ "$ENABLE_V8" == "true" ] && case "$TARGET_CPU" in
         arm)
             echo "v8_snapshot_toolchain = \"//build/toolchain/linux:clang_x86_v8_arm\""