Update libgit2 to v0.27.7 (#30584)

* Update libgit2 to v0.27.7

* Remove problematic portions of the libgit2 patches

These patches make changes to libgit2's .travis.yml file which was
removed when libgit2 switched to Azure Pipelines for CI. Since they are
non-functional changes for us, we can simply remove them from the diff.

NEWS.md

@@ -46,6 +46,7 @@ Standard library changes
 External dependencies
 ---------------------
 
+* libgit2 has been updated to v0.27.7 ([#30584]).
 
 Deprecated or removed
 ---------------------

deps/checksums/libgit2-f23dc5b29f1394928a940d7ec447f4bfd53dad1f.tar.gz/md5

@@ -0,0 +1 @@
+1c2d86e544cb0347d86cbe5210531cf8

deps/checksums/libgit2-f23dc5b29f1394928a940d7ec447f4bfd53dad1f.tar.gz/sha512

@@ -0,0 +1 @@
+531b8a7ae8830eb2dfd36a931b228967b865a19f1d903b75add4201bc503b789d4495b583fbd078734ac7056361b53779ebceb7a439fdcd897396dbc2dd6d4f3

deps/libgit2.version

@@ -1,2 +1,2 @@
-LIBGIT2_BRANCH=v0.27.2
-LIBGIT2_SHA1=8d36dc62ba1b5d7deb66b6f982e005ddbc2ce343
+LIBGIT2_BRANCH=v0.27.7
+LIBGIT2_SHA1=f23dc5b29f1394928a940d7ec447f4bfd53dad1f

deps/patches/libgit2-mbedtls.patch

@@ -2,6 +2,10 @@ Enables MbedTLS support
 
 Upstream: https://github.com/libgit2/libgit2/pull/4173
 
+NOTE: libgit2 has switched its CI to Azure Pipelines. The aforementioned PR makes modifications
+to the Travis YAML file, which has since been removed, causing patch conflicts. That part of
+the diff has thus been removed here.
+
 git diff ca3b2234dc7f1bd0d0f81488d3e29980b47a85b4^..cb2da47e56159faaaf143943c74ffb8f60a988b1 > libgit2-mbedtls.patch
 
 mbedtls: initial support
@@ -20,27 +24,6 @@ cmake: make our preferred backend ordering consistent
 travis: just grab what we need from mbedtls
 travis: pass -fPIC when configuring mbedtls
 
-diff --git a/.travis.yml b/.travis.yml
-index a4c8e91df..b5f1c6ff6 100644
---- a/.travis.yml
-+++ b/.travis.yml
-@@ -55,6 +55,16 @@ matrix:
-          OPTIONS="-DBUILD_CLAR=ON -DBUILD_EXAMPLES=OFF -DDEBUG_POOL=ON -DCMAKE_BUILD_TYPE=Debug"
-      os: linux
-      dist: trusty
-+   - compiler: gcc
-+     env:
-+         MBEDTLS=1
-+         OPTIONS="-DTHREADSAFE=ON -DCMAKE_BUILD_TYPE=Release -DUSE_HTTPS=mbedTLS -DMBEDTLS_ROOT_DIR=../deps/mbedtls"
-+     os: linux
-+   - compiler: gcc
-+     env:
-+         MBEDTLS=1
-+         OPTIONS="-DTHREADSAFE=OFF -DBUILD_EXAMPLES=ON -DUSE_HTTPS=mbedTLS -DMBEDTLS_ROOT_DIR=../deps/mbedtls"
-+     os: linux
-  allow_failures:
-    - env: COVERITY=1
-
 diff --git a/CMakeLists.txt b/CMakeLists.txt
 index 2ca5354a7..9176eee04 100644
 --- a/CMakeLists.txt

deps/patches/libgit2-mbedtls2.patch

@@ -2,25 +2,10 @@ Fixes mbedTLS support to link properly and not include libssl.so
 
 Tracked in upstream PR https://github.com/libgit2/libgit2/pull/4678
 
-diff --git a/.travis.yml b/.travis.yml
-index 686041bfa..61edba135 100644
---- a/.travis.yml
-+++ b/.travis.yml
-@@ -58,12 +58,12 @@ matrix:
-    - compiler: gcc
-      env:
-          MBEDTLS=1
--         OPTIONS="-DTHREADSAFE=ON -DCMAKE_BUILD_TYPE=Release -DUSE_HTTPS=mbedTLS -DMBEDTLS_ROOT_DIR=../deps/mbedtls"
-+         OPTIONS="-DTHREADSAFE=ON -DCMAKE_BUILD_TYPE=Release -DUSE_HTTPS=mbedTLS -DSHA1_BACKEND=mbedTLS -DMBEDTLS_ROOT_DIR=../deps/mbedtls"
-      os: linux
-    - compiler: gcc
-      env:
-          MBEDTLS=1
--         OPTIONS="-DTHREADSAFE=OFF -DBUILD_EXAMPLES=ON -DUSE_HTTPS=mbedTLS -DMBEDTLS_ROOT_DIR=../deps/mbedtls"
-+         OPTIONS="-DTHREADSAFE=OFF -DBUILD_EXAMPLES=ON -DUSE_HTTPS=mbedTLS -DSHA1_BACKEND=mbedTLS -DMBEDTLS_ROOT_DIR=../deps/mbedtls"
-      os: linux
-  allow_failures:
-    - env: COVERITY=1
+NOTE: libgit2 has switched its CI to Azure Pipelines. The aforementioned PR makes modifications
+to the Travis YAML file, which has since been removed, causing patch conflicts. That part of
+the diff has thus been removed here.
+
 diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
 index 2b82bb325..2deed5f87 100644
 --- a/src/CMakeLists.txt