message: If the prefix is recompiled, clzsi2 does not have to be removed.
diff: @@ -97,18 +97,13 @@ $(BUILD)/debug/libc.a: $(BUILD)/debug/librelibc.a $(BUILD)/pthreads-emb/libpthre
  echo "end" >> "$@.mri"
  ar -M < "$@.mri"
  -$(BUILD)/debug/libc.so: $(BUILD)/debug/librelibc.patched.a $(BUILD)/pthreads-emb/libpthread.a $(BUILD)/openlibm/libopenlibm.a
  +$(BUILD)/debug/libc.so: $(BUILD)/debug/librelibc.a $(BUILD)/pthreads-emb/libpthread.a $(BUILD)/openlibm/libopenlibm.a
  $(CC) -nostdlib -shared -Wl,--whole-archive $^ -Wl,--no-whole-archive -o $@
  $(BUILD)/debug/librelibc.a: $(SRC)
  CARGO_INCREMENTAL=0 $(CARGO) rustc $(CARGOFLAGS) -- --emit link=$@ $(RUSTCFLAGS)
  touch $@
  -$(BUILD)/debug/librelibc.patched.a: $(BUILD)/debug/librelibc.a
  - # Patch out clzsi2.o from libgcc
  - cp $< $@
  - ar d $@ clzsi2.o
  -
  $(BUILD)/debug/crt0.o: $(SRC)
  CARGO_INCREMENTAL=0 $(CARGO) rustc --manifest-path src/crt0/Cargo.toml $(CARGOFLAGS) -- --emit obj=$@ -C panic=abort $(RUSTCFLAGS)
  touch $@
  @@ -139,18 +134,13 @@ $(BUILD)/release/libc.a: $(BUILD)/release/librelibc.a $(BUILD)/pthreads-emb/libp
  echo "end" >> "$@.mri"
  ar -M < "$@.mri"
  -$(BUILD)/release/libc.so: $(BUILD)/release/librelibc.patched.a $(BUILD)/pthreads-emb/libpthread.a $(BUILD)/openlibm/libopenlibm.a
  +$(BUILD)/release/libc.so: $(BUILD)/release/librelibc.a $(BUILD)/pthreads-emb/libpthread.a $(BUILD)/openlibm/libopenlibm.a
  $(CC) -nostdlib -shared -Wl,--whole-archive $^ -Wl,--no-whole-archive -o $@
  $(BUILD)/release/librelibc.a: $(SRC)
  CARGO_INCREMENTAL=0 $(CARGO) rustc --release $(CARGOFLAGS) -- --emit link=$@ $(RUSTCFLAGS)
  touch $@
  -$(BUILD)/release/librelibc.patched.a: $(BUILD)/release/librelibc.a
  - # Patch out clzsi2.o from libgcc
  - cp $< $@
  - ar d $@ clzsi2.o
  -
  $(BUILD)/release/crt0.o: $(SRC)
  CARGO_INCREMENTAL=0 $(CARGO) rustc --release --manifest-path src/crt0/Cargo.toml $(CARGOFLAGS) -- --emit obj=$@ -C panic=abort $(RUSTCFLAGS)
  touch $@
  