contrib/expat: update libexpat from 2.6.0 to 2.7.1
Changes: https://github.com/libexpat/libexpat/blob/R_2_7_1/expat/Changes
Note that libbsdxml(3) is only intended to used by utilities in the
FreeBSD base system. None of the vulnerabilities addressed by expat
releases 2.6.1 - 2.7.1 is exploitable on FreeBSD as supported by the
security-officer@ team.
Approved by: so
Security: FreeBSD-EN-25:05.expat
Security: CVE-2024-8176
Security: CVE-2024-50602
Security: CVE-2024-45490, CVE-2024-45491, CVE-2024-45492
Security: CVE-2024-28757
(cherry picked from commit ffd294a1f4c23863c3e515d16dce31d5509bcb01)
(cherry picked from commit bab279022ba2bed4f216924b3b5fdfc60ced364c)
(cherry picked from commit ba23ab2168ffabc2c5e647a1a37ab9a8fb482bb8)
(cherry picked from commit eab7ed2ec2af6307842abcc94c11743a1058bd11)
(cherry picked from commit 908f215e80fa482aa953c39afa6bb516f561fc00)
(cherry picked from commit 3d46113d21963d4236506f7c8e9c476b1f4aa512)
(cherry picked from commit fe9278888fd4414abe2d922e469cf608005f4c65)
(cherry picked from commit 41b768ae1970ed484abaaea401453c3902df93c2)
(cherry picked from commit 03a1992591b0ae85b6b250255fe56e17f6d919c6)
(cherry picked from commit adc9e9e8dbddcf7d57bcdef0d9d0a0e7c08c15ba)
(cherry picked from commit 00c8538e87c61f1fd57ccd9e02a6d435b68d9a73)
(cherry picked from commit 5630672e6f6d58597a3d6f01928a7703f1cdd207)