Suppress some Mac-specific linker warnings.

[david-german-tri]

Contributes to #5183.

@liangfok for feature review.

---

This change is 

[liangfok]

I just did a clean build on OSX and encountered both "compact unwind" and, surprisingly, "pthread" warnings:

https://gist.github.com/liangfok/a4efc3c5cf4400aaa5d14fbc23deb051

I'm surprised because I was fairly sure the pthread warnings were addressed by #5333.

---

Reviewed 1 of 1 files at r1.
Review status: all files reviewed at latest revision, all discussions resolved.

---

Comments from Reviewable

[liangfok]

^^^ I'm using 4c12faa.

---

Review status: all files reviewed at latest revision, all discussions resolved.

---

Comments from Reviewable

[david-german-tri]

encountered both "compact unwind"

Are you sure? I don't see any of those after you do git checkout ct in your gist.

---

Review status: all files reviewed at latest revision, all discussions resolved.

---

Comments from Reviewable

[david-german-tri]

I can reproduce the pthread warnings. Looking into that now, but it's unrelated to this PR.

---

Review status: all files reviewed at latest revision, all discussions resolved.

---

Comments from Reviewable

[liangfok]

Here is an example of the "compact unwind" warning from my gist:

INFO: From Linking drake/solvers/mathematical_program_test:
ld: warning: could not create compact unwind for ___dmumps_parallel_analysis_MOD_dmumps_715: stack subq instruction is too different from dwarf stack size
ld: warning: could not create compact unwind for _write_float: stack subq instruction is too different from dwarf stack size

Based on my web browser's search bar, there are 87 instances of it in the gist.

---

Review status: all files reviewed at latest revision, all discussions resolved.

---

Comments from Reviewable

[liangfok]

Oh, sorry, I must have accidentally mixed up two outputs into a single gist. I think you're right.

---

Review status: all files reviewed at latest revision, all discussions resolved.

---

Comments from Reviewable

[david-german-tri]

+@jwnimmer-tri for platform review.

---

Review status: all files reviewed at latest revision, all discussions resolved.

---

Comments from Reviewable

[jwnimmer-tri]

---

Reviewed 1 of 1 files at r1.
Review status: all files reviewed at latest revision, all discussions resolved.

---

Comments from Reviewable