Update to latest BearSSL code.

[earlephilhower]

No description provided.

[earlephilhower]

commit 67786877341aac98c62e3b765fc64f4c49d81370 (HEAD -> update, origin/update)
Author: Earle F. Philhower, III <[email protected]>
Date:   Fri Jan 25 10:11:52 2019 -0800

    Fix pgm_read_float macro

commit 8f2e46962daf9347a395a3ff4ec50237ca3a2353
Merge: 79edbc8 c1bb535
Author: Earle F. Philhower, III <[email protected]>
Date:   Fri Jan 25 10:10:18 2019 -0800

    Merge branch 'master' of https://www.bearssl.org/git/BearSSL into HEAD

commit c1bb5356bb52984178c269886b6835b532ef30c2 (upstream/master)
Author: Thomas Pornin <[email protected]>
Date:   Thu Jan 24 22:07:19 2019 +0100

    Small workaround for CompCert compatibility.

commit 87a796dd69fcdbd1c0dd7594f3ddb16c90abee5e
Author: Thomas Pornin <[email protected]>
Date:   Tue Jan 22 00:04:08 2019 +0100

    Fixed computing of intermediate buffer size for maximum-size RSA keys.