bazel should improve consistency behavior when as a external repo

[xiedeacc]

Description of the feature request:

I wrote a BUILD script for libsodium work well under libsodium source tree, build failed for search path in copts seems relative to workspace when it as an external repo, but cc_library's hdrs and srcs is ralative to libsodium source directory, these inconsistent behaviors really made me confused , in fact I think this is a bug, if made copt behavior same bettween external and it self, it can avoid many silly things, really hope guys can change this behavior, really realy thanks!!!!

demo:
https://github.com/xiedeacc/libsodium.git
https://github.com/xiedeacc/bazel_problem.git (libsodium imported in bazel_problem )

workspace(name = "bazel_problem")
...
new_git_repository(
    name = "libsodium",
    build_file = "//bazel_script:libsodium.BUILD",
    remote = "[email protected]:jedisct1/libsodium.git",
    tag = "1.0.20-RELEASE",
)
...

libsodium.BUILD

package(default_visibility = ["//visibility:public"])
...


COMMON_COTPS = [
    "-g3",
    "-pthread",
    "-fvisibility=hidden",
    "-fPIC",
    "-fno-strict-aliasing",
    "-fno-strict-overflow",
    "-fstack-protector",
    "-Wno-deprecated-declarations",
    "-Wno-unknown-pragmas",
    "-ftls-model=local-dynamic",
    "-Isrc/libsodium/include/sodium",
    "-Isrc/libsodium/crypto_aead/aegis128l",
    "-Isrc/libsodium/crypto_aead/aegis256",
    "-Isrc/libsodium/crypto_core/ed25519/ref10/fe_25_5",
    "-Isrc/libsodium/crypto_core/ed25519/ref10/fe_51",
    "-Isrc/libsodium/crypto_generichash/blake2b/ref",
    "-Isrc/libsodium/crypto_onetimeauth/poly1305",
    "-Isrc/libsodium/crypto_onetimeauth/poly1305/donna",
    "-Isrc/libsodium/crypto_onetimeauth/poly1305/sse2",
    "-Isrc/libsodium/crypto_pwhash/argon2",
    "-Isrc/libsodium/crypto_pwhash/scryptsalsa208sha256",
    "-Isrc/libsodium/crypto_pwhash/scryptsalsa208sha256/nosse",
    "-Isrc/libsodium/crypto_scalarmult/curve25519",
    "-Isrc/libsodium/crypto_scalarmult/curve25519/ref10",
    "-Isrc/libsodium/crypto_scalarmult/curve25519/sandy2x",
    "-Isrc/libsodium/crypto_shorthash/siphash24/ref",
    "-Isrc/libsodium/crypto_sign/ed25519/ref10",
    "-Isrc/libsodium/crypto_stream/chacha20",
    "-Isrc/libsodium/crypto_stream/chacha20/dolbeau",
    "-Isrc/libsodium/crypto_stream/chacha20/ref",
    "-Isrc/libsodium/crypto_stream/salsa20",
    "-Isrc/libsodium/crypto_stream/salsa20/ref",
    "-Isrc/libsodium/crypto_stream/salsa20/xmm6",
    "-Isrc/libsodium/crypto_stream/salsa20/xmm6int",
]
...
cc_library(
    name = "sodium",
    srcs = [
        "src/libsodium/sodium/codecs.c",
        "src/libsodium/sodium/core.c",
        "src/libsodium/sodium/runtime.c",
    ],
    hdrs = glob([
        "src/libsodium/include/sodium/*.h",
        "src/libsodium/include/sodium/private/*.h",
    ]),
    copts = select({
        ":windows": [],
        "//conditions:default": [
            "-msse2",
            "-mssse3",
        ] + COMMON_COTPS,
    }),
    includes = [
    ],
    linkopts = select({
        ":windows": [],
        "//conditions:default": [
            "-Wl,-z,relro",
            "-Wl,-z,now",
            "-Wl,-z,noexecstack",
            "-export-dynamic",
        ],
    }),
    local_defines = COMMON_DEFINES,
    visibility = ["//visibility:public"],
    deps = [
        ":aesni",
        ":armcrypto",
        ":avx2",
        ":avx512f",
        ":common",
        ":rdrand",
        ":sse2",
        ":sse41",
        ":ssse3",
    ],
)