[build] Modernize Bazel spelling for selecting compiler flags

[jwnimmer-tri]

Deprecate the @cc external.

Towards #20731. Keeping this repository rule intact with bzlmod is certainly possible, but is somewhat of a pain point and hassle. Better to just use what rules_cc already offers for compiler selection as best we can.

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This change is 

[jwnimmer-tri]

Reviewable status: needs platform reviewer assigned, needs at least two assigned reviewers

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tools/workspace/fcl_internal/package.BUILD.bazel line 128 at r3 (raw file):

    copts = [
        "-fvisibility=hidden",
        "-w",

FYI This -w flag is not required / affected by this patch. While locally testing permutations of options, I noticed that there were spurious warnings coming from FCL builds, so this suppresses them. The spurious warning were also there on master.

[jwnimmer-tri]

+@xuchenhan-tri for feature review, please.

[xuchenhan-tri]

Reviewed 4 of 9 files at r1, 6 of 7 files at r2, 2 of 2 files at r3, all commit messages.
Reviewable status: 2 unresolved discussions, needs at least two assigned reviewers

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tools/workspace/default.bzl line 162 at r3 (raw file):

        buildifier_repository(name = "buildifier", mirrors = mirrors)
    if "cc" not in excludes:
        # Deprecated 2025-04-01.

Btw this is less than 3 months if we care

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tools/cc_toolchain/BUILD.bazel line 110 at r3 (raw file):

int_flag(
    name = "compiler_major",
    build_setting_default = 0,

Btw is the default never used here?

[jwnimmer-tri]

+@SeanCurtis-TRI for platform review per schedule, but if today is too busy feel free to spill it to Grant.

Reviewed 4 of 4 files at r4, all commit messages.
Reviewable status: 1 unresolved discussion, LGTM missing from assignee SeanCurtis-TRI(platform)

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tools/cc_toolchain/BUILD.bazel line 110 at r3 (raw file):

Previously, xuchenhan-tri wrote…

Btw is the default never used here?

The default would be used in case the user is building Drake on an unsupported platform, or if the user is building Drake as a bazel module external.

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tools/workspace/default.bzl line 162 at r3 (raw file):

Previously, xuchenhan-tri wrote…

Btw this is less than 3 months if we care

Oops, I'd bumped the date out to May in the warning printout but missed this comment.

[SeanCurtis-TRI]

Reviewed 3 of 9 files at r1, 5 of 7 files at r2, 4 of 4 files at r4, all commit messages.
Reviewable status: 3 unresolved discussions

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tools/skylark/drake_cc.bzl line 115 at r4 (raw file):

def _platform_copts(rule_copts, rule_gcc_copts, rule_clang_copts, cc_test = 0):
    """Returns the concatenation of Drake's platform-specific BASE_COPTS,
    plus the passed-in rule_copts, plus the passed-in plus rule_{cc}_copts iff

nit: vestigial "plus"?

"..., plus the passed-in plus rule_{cc}_copts iff..."

Code quote:

plus

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tools/skylark/drake_cc.bzl line 119 at r4 (raw file):

    When cc_test=1, the GCC_CC_TEST_FLAGS will also be added. It should only be
    used from cc_test rules or rules that are boil down to cc_test rules.

nit: grammar

Suggestion:

rules that boil down 

[jwnimmer-tri]

Reviewed 2 of 2 files at r5, all commit messages.
Reviewable status: complete! all discussions resolved, LGTM from assignees SeanCurtis-TRI(platform),xuchenhan-tri(platform)

[SeanCurtis-TRI]

Reviewed 2 of 2 files at r5, all commit messages.
Reviewable status: complete! all discussions resolved, LGTM from assignees SeanCurtis-TRI(platform),xuchenhan-tri(platform)