[tools] Link ignition-math statically

[jwnimmer-tri]

It was an oddball in terms of being a shared library. Most all of our other private dependencies are currently being linked statically. For simplicity, we prefer that the only dependencies linked as shared are either public dependencies (such as spdlog) and/or LGPL'd (such as lcm).

Partially reverts #7622.

Tested locally that:

• ls -l bazel-bin/external/ignition_math/libdrake_ignition_math.so shows a non-empty size
• The installed copy of lib/libdrake_ignition_math.so after a bazel run //:install shows a non-empty size.
• The ignition headers and cmake config file are still being installed.

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This change is 

[jwnimmer-tri]

@drake-jenkins-bot mac-catalina-clang-bazel-experimental-release please

[jwnimmer-tri]

+@rpoyner-tri for feature review, please?

[rpoyner-tri]

Reviewed 2 of 5 files at r1, 4 of 4 files at r2, all commit messages.
Reviewable status: LGTM missing from assignee rpoyner-tri(platform), needs at least two assigned reviewers (waiting on @jwnimmer-tri)

[rpoyner-tri]

Reviewable status: needs at least two assigned reviewers (waiting on @jwnimmer-tri)

[SeanCurtis-TRI]

+@SeanCurtis-TRI

Reviewable status: LGTM missing from assignee SeanCurtis-TRI(platform) (waiting on @SeanCurtis-TRI)

[SeanCurtis-TRI]

Reviewed 2 of 5 files at r1, 2 of 4 files at r2, all commit messages.
Reviewable status: complete! all discussions resolved, LGTM from assignees rpoyner-tri(platform),SeanCurtis-TRI(platform) (waiting on @jwnimmer-tri)

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tools/workspace/ignition_math/package.BUILD.bazel, line 237 at r2 (raw file):

    }),
    linkshared = 1,
    linkstatic = 1,

BTW For my own edification, what is the implication of simultaneously declaring linkshared and linkstatic?

[jwnimmer-tri]

Reviewable status: complete! all discussions resolved, LGTM from assignees rpoyner-tri(platform),SeanCurtis-TRI(platform) (waiting on @jwnimmer-tri)

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tools/workspace/ignition_math/package.BUILD.bazel, line 237 at r2 (raw file):

Previously, SeanCurtis-TRI (Sean Curtis) wrote…

BTW For my own edification, what is the implication of simultaneously declaring linkshared and linkstatic?

https://docs.bazel.build/versions/4.2.0/be/c-cpp.html#cc_binary.linkshared

"linkshared" means to create a shared library.

"linkstatic" means that the deps should come in as *.a files (object code copied into the new *.so), not as references to more *.so files.