[Bug]: Headers present in the sysroot but not available in the bazel sandbox about gcc-toolchain

[kriswuollett]

As mentioned in #134, I've encountered same issue here for stddef.h which should be in "-isystemexternal/sysroot_aarch64//lib/gcc/aarch64-linux/10.3.0/include". When I patch the gcc-toolchain repo to also include /usr/include/linux I see it in the invocation, "-isystemexternal/sysroot_aarch64//usr/include/linux" but still can't find it:

running: "/home/kris/.cache/bazel/_bazel_kris/ebd20a16b5bb6af41a7a481997cc3984/sandbox/linux-sandbox/1077/execroot/my-code/external/gcc_toolchain_aarch64/bin/gcc" "-O0" "-ffunction-sections" "-fdata-sections" "-fPIC" "-gdwarf-4" "-fno-omit-frame-pointer" "--sysroot" "external/sysroot_aarch64" "-no-canonical-prefixes" "-fno-canonical-system-headers" "-Wno-builtin-macro-redefined" "-D__DATE__=\"redacted\"" "-D__TIMESTAMP__=\"redacted\"" "-D__TIME__=\"redacted\"" "-fdiagnostics-color=always" "-nostdinc" "-Bexternal/gcc_toolchain_aarch64/bin" "-isystemexternal/sysroot_aarch64//aarch64-linux/include/c++/10.3.0" "-isystemexternal/sysroot_aarch64//aarch64-linux/include/c++/10.3.0/aarch64-linux" "-isystemexternal/sysroot_aarch64//lib/gcc/aarch64-linux/10.3.0/include-fixed" "-isystemexternal/sysroot_aarch64//lib/gcc/aarch64-linux/10.3.0/include" "-isystemexternal/sysroot_aarch64//usr/include" "-isystemexternal/sysroot_aarch64//usr/include/linux" "-I" "zstd/lib/" "-I" "zstd/lib/common" "-fvisibility=hidden" "-ffunction-sections" "-fdata-sections" "-fmerge-all-constants" "-DZSTD_LIB_DEPRECATED=0" "-DXXH_PRIVATE_API=" "-DZSTDLIB_VISIBILITY=" "-DZSTDERRORLIB_VISIBILITY=" "-o" "/home/kris/.cache/bazel/_bazel_kris/ebd20a16b5bb6af41a7a481997cc3984/sandbox/linux-sandbox/1077/execroot/my-code/bazel-out/k8-fastbuild-ST-87f845362927/bin/external/crate_index__zstd-sys-2.0.7-zstd.1.5.4/zstd-sys_build_script.out_dir/zstd/lib/common/error_private.o" "-c" "zstd/lib/common/error_private.c"
cargo:warning=In file included from zstd/lib/common/error_private.h:24,
cargo:warning=                 from zstd/lib/common/error_private.c:13:
cargo:warning=zstd/lib/common/../zstd_errors.h:19:10: fatal error: stddef.h: No such file or directory
cargo:warning=   19 | #include <stddef.h>   /* size_t */
cargo:warning=      |          ^~~~~~~~~~
cargo:warning=compilation terminated.
exit status: 1