为什么此Makefile仅适用于单个作业？

我正在尝试编写一个Makefile可编译交叉编译器的。它下载GCC并binutils解压缩档案，运行configure脚本并运行make。

这是Makefile我写的：

# Versions
GCC_VERSION := 6.3.0
BINUTILS_VERSION := 2.27

# Build
TARGET ?= i686-elf
PREFIX := $(realpath build)

# Phony tasks
.PHONY: all clean gcc binutils

# Targets
BINUTILS_TARGETS := build/bin/${TARGET}-addr2line build/bin/${TARGET}-ar \
    build/bin/${TARGET}-as build/bin/${TARGET}-c++filt \
    build/bin/${TARGET}-elfedit build/bin/${TARGET}-gprof \
    build/bin/${TARGET}-ld build/bin/${TARGET}-ld.bfd build/bin/${TARGET}-nm \
    build/bin/${TARGET}-objcopy build/bin/${TARGET}-objdump \
    build/bin/${TARGET}-ranlib build/bin/${TARGET}-readelf \
    build/bin/${TARGET}-size build/bin/${TARGET}-strings \
    build/bin/${TARGET}-strip
GCC_TARGETS := build/bin/${TARGET}-cpp build/bin/${TARGET}-gcc \
    build/bin/${TARGET}-gcc-${GCC_VERSION} build/bin/${TARGET}-gcc-ar \
    build/bin/${TARGET}-gcc-nm build/bin/${TARGET}-gcc-ranlib \
    build/bin/${TARGET}-gcov build/bin/${TARGET}-gcov-tool

# Aliases
all: binutils gcc
gcc: ${GCC_TARGETS}
binutils: ${BINUTILS_TARGETS}

# Download the packages
packages/gcc-${GCC_VERSION}.tar.bz2:
    curl ftp://ftp.gnu.org/gnu/gcc/gcc-${GCC_VERSION}/gcc-${GCC_VERSION}.tar.bz2 \
        -o $@
packages/binutils-${BINUTILS_VERSION}.tar.bz2:
    curl ftp://ftp.gnu.org/gnu/binutils/binutils-${BINUTILS_VERSION}.tar.bz2 \
        -o $@

# Extract them
packages/gcc-${GCC_VERSION}/configure: packages/gcc-${GCC_VERSION}.tar.bz2
    tar -xmjf $< -C packages
packages/binutils-${BINUTILS_VERSION}/configure: packages/binutils-${BINUTILS_VERSION}.tar.bz2
    tar -xmjf $< -C packages

# Build them
${GCC_TARGETS}: packages/gcc-${GCC_VERSION}/configure
    mkdir -p build/gcc
    cd build/gcc && ../../packages/gcc-${GCC_VERSION}/configure \
        --target=${TARGET} --prefix=${PREFIX} --disable-nls \
        --enable-languages=c --without-headers && make all-gcc && \
        make all-target-libgcc && make install-gcc && make install-target-libgcc
${BINUTILS_TARGETS}: packages/binutils-${BINUTILS_VERSION}/configure
    mkdir -p build/binutils
    cd build/binutils && ../../packages/binutils-${BINUTILS_VERSION}/configure \
        --target=${TARGET} --prefix=${PREFIX} --with-sysroot --disable-nls \
        --disable-werror && make && make install

# Clean everything
clean:
    rm -rf build/*
    rm -rf packages/*

它在make没有选项的情况下运行时可以工作，但是当我使用Jobs选项时，它会失败（但并非每次都失败）：它会下载binutils并GCC并行运行。

完全下载binutils后，它将解压缩并进行编译，然后GCC下载结束，但它不会执行任何操作，也没有错误。

有时也可能会编译GCC或binutils失败，并出现奇怪的错误（我将使用其中的一些内容来编辑这篇文章）。