When a test is in the FEATURE_TESTS_BASIC list in tools/build/Makefile.feature
must be added to tools/build/feature/test-all.c, because the successfull
compilation and linking of that test-all.bin file means that all the
features listed in FEATURE_TESTS_BASIC are present in the system, so we
don't have to go on feature by feature test building them.

Since reallocarray() is expected to be present in modern systems, it has
a place in FEATURE_TESTS_BASIC, so that we speed up the build process
building just that file.

For older systems, such as ubuntu:16.04 (build failure reported by Jin
Yao) debian:8, and for the current flagship RHEL distro, RHEL7, the
build will fail as test-all.bin (without test-reallocarray.c included)
passes but reallocarray() isn't present, making the build fail with:

    CC       /tmp/build/perf/libbpf.o
    MKDIR    /tmp/build/perf/fs/
    CC       /tmp/build/perf/fs/tracing_path.o
    LD       /tmp/build/perf/fd/...