espeak-ng: explicitly disable parallel building
espeak-ng: explicitly disable parallel building

Current release lacks dependencies on local espeak-ng:

    cd dictsource && ESPEAK_DATA_PATH=/build/espeak-ng LD_LIBRARY_PATH=../src: \
        ../src/espeak-ng --compile=yue && cd ..
    bash: line 1: ../src/espeak-ng: No such file or directory

Should be fixed in next release: https://github.com/espeak-ng/espeak-ng/pull/1029
Can't apply patch as is as Makefile.am diverged quite a bit since 1.50
release.

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