Switch to clang-format-10 to support more recent platforms

clang-format-7 (or older) might not even be available anymore on some
systems, and will certainly not be the default. clang-format-10 has
improved support for initializer lists, resulting in different
formatting of these:
```
foo bar{value_1,
        value_2};
```
now is formatted as
```
foo bar{
  value_1,
  value_2};
```
which is more consistent with how the same would have been formatted
had parentheses been used.

clang-format-10 is even available on Ubuntu 18.04, which is the most
dated system our CI builds are still running on.

Fixes: #6457

Author: tautschnig

.clang-format

@@ -58,7 +58,7 @@ SpacesInCStyleCastParentheses: 'false'
 SpacesInContainerLiterals: 'false'
 SpacesInParentheses: 'false'
 SpacesInSquareBrackets: 'false'
-Standard: Cpp11
+Standard: c++11
 TabWidth: '2'
 UseTab: Never
 ---

.github/workflows/pull-request-check-clang-format.sh

@@ -7,7 +7,7 @@ set -e
 echo "Pull request's base branch is: ${BASE_BRANCH}"
 echo "Pull request's merge branch is: ${MERGE_BRANCH}"
 echo "Pull request's source branch is: ${GITHUB_HEAD_REF}"
-clang-format-7 --version
+clang-format-10 --version
 
 # The checkout action leaves us in detatched head state. The following line
 # names the checked out commit, for simpler reference later.
@@ -26,7 +26,7 @@ echo "Checking for formatting errors introduced since $MERGE_BASE"
 
 # Do the checking. "eval" is used so that quotes (as inserted into $EXCLUDES
 # above) are not interpreted as parts of file names.
-eval git-clang-format-7 --binary clang-format-7 $MERGE_BASE -- $EXCLUDES
+eval git-clang-format --binary clang-format-10 $MERGE_BASE -- $EXCLUDES
 git diff > formatted.diff
 if [[ -s formatted.diff ]] ; then
   echo 'Formatting error! The following diff shows the required changes'

.github/workflows/pull-request-checks.yaml

@@ -502,8 +502,8 @@ jobs:
           DEBIAN_FRONTEND: noninteractive
         run: |
           sudo apt-get update
-          sudo apt-get install --no-install-recommends -yq clang-format-7
-      - name: Check updated lines of code match clang-format-7 style
+          sudo apt-get install --no-install-recommends -yq clang-format
+      - name: Check updated lines of code match clang-format-10 style
         env:
           BASE_BRANCH: ${{ github.base_ref }}
           MERGE_BRANCH: ${{ github.ref }}

CODING_STANDARD.md

@@ -340,13 +340,13 @@ To avoid waiting until you've made a PR to find formatting issues, you can
 install clang-format locally and run it against your code as you are working.
 
 Different versions of clang-format have slightly different behaviors. CBMC uses
-clang-format-7 as it is available the repositories for Ubuntu 18.04 and
+clang-format-10 as it is available the repositories for Ubuntu 18.04 and
 Homebrew.
 To install on a Unix-like system, try installing using the system package
 manager:
 ```
-apt-get install clang-format-7  # Run this on Ubuntu, Debian etc.
-brew install clang-format@7     # Run this on a Mac with Homebrew installed
+apt-get install clang-format-10  # Run this on Ubuntu, Debian etc.
+brew install clang-format@10     # Run this on a Mac with Homebrew installed
 ```
 
 If your platform doesn't have a package for clang-format, you can download a
@@ -358,12 +358,12 @@ the [LLVM Snapshot Builds page](http://llvm.org/builds/).
 
 ### FORMATTING A RANGE OF COMMITS
 
-Clang-format is distributed with a driver script called git-clang-format-7.
+Clang-format is distributed with a driver script called git-clang-format.
 This script can be used to format git diffs (rather than entire files).
 
 After committing some code, it is recommended to run:
 ```
-git-clang-format-7 upstream/develop
+git-clang-format upstream/develop
 ```
 *Important:* If your branch is based on a branch other than `upstream/develop`,
 use the name or checksum of that branch instead. It is strongly recommended to
@@ -373,7 +373,7 @@ rebase your work onto the tip of the branch it's based on before running
 Note: By default, git-clang-format uses the git config variable
 `clangformat.binary`. If you have multiple versions of clang-format installed,
 you might need to update this, or explicitly specify the binary to use via
-`--binary clang-format-7`.
+`--binary clang-format-10`.
 
 ### RETROACTIVELY FORMATTING INDIVIDUAL COMMITS
 
@@ -385,7 +385,7 @@ The following command will stop at each commit in the range and run
 clang-format on the diff at that point.  This rewrites git history, so it's
 *unsafe*, and you should back up your branch before running this command:
 ```
-git filter-branch --tree-filter 'git-clang-format-7 upstream/develop' \
+git filter-branch --tree-filter 'git-clang-format upstream/develop' \
   -- upstream/develop..HEAD
 ```
 *Important*: `upstream/develop` should be changed in *both* places in the