build: move errExit macro into inline function

[kmk3]

Move most of the errExit macro into a new _errExit inline function
and use the former just to forward arguments to the latter.

This reduces the noise in the build output when using -fanalyzer, as
it causes the errExit macro to stop being expanded.

For example, the complete output of the following warning in
src/firejail/dbus.c is reduced from 243 lines to 141 lines (a ~41%
reduction):

$ pacman -Q gcc
gcc 13.2.1-5
$ ./configure --enable-apparmor --enable-analyzer >/dev/null &&
  make clean >/dev/null && make >/dev/null
[...]
../../src/firejail/dbus.c: In function ‘dbus_proxy_start’:
../../src/firejail/dbus.c:311:36: warning: leak of file descriptor ‘dup2(output_fd, 1)’ [CWE-775] [-Wanalyzer-fd-leak]
  311 |                                 if (dup2(output_fd, STDOUT_FILENO) != STDOUT_FILENO)
[...]
         ‘dbus_create_user_dir’: event 5
           |
           |../../src/firejail/../include/common.h:42:25:
           |   42 | #define errExit(msg) do { \
           |      |                         ^
           |      |                         |
           |      |                         (5) ...to here
../../src/firejail/dbus.c:239:17: note: in expansion of macro ‘errExit’
           |  239 |                 errExit("asprintf");
           |      |                 ^~~~~~~
[...]

Relates to #6190.

[kmk3]

Note: This also fixes hundreds of (seemingly false positive) warnings when
using cppcheck 2.12.0-2 on Artix Linux:

On commit 092bb0a ("build(deps): bump github/codeql-action from 3.24.0 to
3.24.3", 2024-02-19) / PR #6214:

$ make clean >/dev/null &&
  cppcheck --force --error-exitcode=1 --enable=warning,performance \
  -i src/firejail/checkcfg.c -i src/firejail/main.c .
Checking src/etc-cleanup/main.c ...
Checking src/etc-cleanup/main.c: __FUNCTION__;__func__...
src/etc-cleanup/main.c:73:3: warning: %s in format string (no. 3) requires 'char *' but the argument type is 'signed int'. [invalidPrintfArgType_s]
  errExit("strdup");
  ^
1/149 files checked 0% done
Checking src/fbuilder/build_bin.c ...
Checking src/fbuilder/build_bin.c: __FUNCTION__;__func__...
src/fbuilder/build_bin.c:108:4: warning: %s in format string (no. 3) requires 'char *' but the argument type is 'signed int'. [invalidPrintfArgType_s]
   errExit("asprintf");
   ^
2/149 files checked 0% done
Checking src/fbuilder/build_fs.c ...
Checking src/fbuilder/build_fs.c: __FUNCTION__;__func__...
src/fbuilder/build_fs.c:118:4: warning: %s in format string (no. 3) requires 'char *' but the argument type is 'signed int'. [invalidPrintfArgType_s]
   errExit("asprintf");
   ^
src/fbuilder/build_fs.c:294:3: warning: %s in format string (no. 3) requires 'char *' but the argument type is 'signed int'. [invalidPrintfArgType_s]
  errExit("asprintf");
  ^
3/149 files checked 1% done
[...]
$ make clean >/dev/null &&
  cppcheck -q --force --error-exitcode=1 --enable=warning,performance \
  -i src/firejail/checkcfg.c -i src/firejail/main.c . | grep 'warning:' | wc -l
684

On commit 5c65577 ("Merge pull request #6217 from kmk3/build-errexit-func",
2024-02-23):

$ make clean >/dev/null &&
  cppcheck --force --error-exitcode=1 --enable=warning,performance \
  -i src/firejail/checkcfg.c -i src/firejail/main.c .
Checking src/etc-cleanup/main.c ...
Checking src/etc-cleanup/main.c: __FUNCTION__;__func__...
1/149 files checked 0% done
Checking src/fbuilder/build_bin.c ...
Checking src/fbuilder/build_bin.c: __FUNCTION__;__func__...
2/149 files checked 0% done
Checking src/fbuilder/build_fs.c ...
Checking src/fbuilder/build_fs.c: __FUNCTION__;__func__...
3/149 files checked 1% done
[...]
$ make clean >/dev/null &&
  cppcheck -q --force --error-exitcode=1 --enable=warning,performance \
  -i src/firejail/checkcfg.c -i src/firejail/main.c . | grep 'warning:' | wc -l
0

CI is currently not affected, as older versions of cppcheck are used.

From the runs of commit 092bb0a ("build(deps): bump github/codeql-action from
3.24.0 to 3.24.3", 2024-02-19) / PR #6214:

From cppcheck:

https://github.com/netblue30/firejail/actions/runs/7964810742/job/21743097070:

##[group]Run cppcheck --version
cppcheck --version
shell: /usr/bin/bash -e {0}
##[endgroup]
Cppcheck 2.7
##[group]Run cppcheck -q --force --error-exitcode=1 --enable=warning,performance -i src/firejail/checkcfg.c -i src/firejail/main.c .
cppcheck -q --force --error-exitcode=1 --enable=warning,performance -i src/firejail/checkcfg.c -i src/firejail/main.c .
shell: /usr/bin/bash -e {0}
##[endgroup]
Post job cleanup.

From cppcheck_old:

https://github.com/netblue30/firejail/actions/runs/7961492382/job/21732847902:

##[group]Run cppcheck --version
cppcheck --version
shell: /usr/bin/bash -e {0}
##[endgroup]
Cppcheck 1.90
##[group]Run cppcheck -q --force --error-exitcode=1 --enable=warning,performance .
cppcheck -q --force --error-exitcode=1 --enable=warning,performance .
shell: /usr/bin/bash -e {0}
##[endgroup]
Post job cleanup.