meson: Regression: systemd is failing to compile with clang-{10,11,12} with --optimization=3 -Db_lto=true

Describe the bug Since meson-0.57.0 was released systemd has been failing to compile with --optimization=3 -Db_lto=true with

FAILED: src/basic/libbasic-gcrypt.a.p/gcrypt-util.c.o 
clang-10 -Isrc/basic/libbasic-gcrypt.a.p -Isrc/basic -I../src/basic -Isrc/fundamental -I../src/fundamental -Isrc/systemd -I../src/systemd -I. -I.. -flto -flto-jobs=0 -Xclang -fcolor-diagnostics -pipe -D_FILE_OFFSET_BITS=64 -Wall -Winvalid-pch -Wextra -Werror -std=gnu99 -O3 -g -Wno-unused-parameter -Wno-missing-field-initializers -Wno-unused-result -Werror=undef -Wmissing-include-dirs -Wold-style-definition -Wpointer-arith -Winit-self -Wfloat-equal -Werror=missing-prototypes -Werror=implicit-function-declaration -Werror=missing-declarations -Werror=return-type -Werror=incompatible-pointer-types -Werror=format=2 -Wstrict-prototypes -Wredundant-decls -Wmissing-noreturn -Wshadow -Wendif-labels -Wstrict-aliasing=2 -Wwrite-strings -Werror=overflow -Werror=shift-count-overflow -Wdate-time -Wnested-externs '-Wno-error=#warnings' -Wno-string-plus-int -ffast-math -fno-common -fdiagnostics-show-option -fno-strict-aliasing -fvisibility=hidden -fstack-protector -fstack-protector-strong --param=ssp-buffer-size=4 -Wno-typedef-redefinition -Wno-gnu-variable-sized-type-not-at-end -Werror=shadow -include config.h -Werror -fPIC -fvisibility=default -MD -MQ src/basic/libbasic-gcrypt.a.p/gcrypt-util.c.o -MF src/basic/libbasic-gcrypt.a.p/gcrypt-util.c.o.d -o src/basic/libbasic-gcrypt.a.p/gcrypt-util.c.o -c ../src/basic/gcrypt-util.c
clang: error: argument unused during compilation: '-flto-jobs=0' [-Werror,-Wunused-command-line-argument]
[29/1801] Generating errno-from-name.h with a custom command (wrapped by meson to capture output)
[30/1801] Generating errno-to-name.h with a custom command (wrapped by meson to capture output)
ninja: build stopped: subcommand failed.
+ fatal ''\''meson compile'\'' failed with --optimization=3 -Db_lto=true'
+ echo -e '\033[31;1m'\''meson compile'\'' failed with --optimization=3 -Db_lto=true\033[0m'
'meson compile' failed with --optimization=3 -Db_lto=true
+ exit 1

To Reproduce The script building systemd can be found at https://github.com/systemd/systemd/blob/main/.github/workflows/build_test.sh. It runs something like

git clone https://github.com/systemd/systemd
cd systemd
AR=llvm-ar-10 CFLAGS=-Werror CXXFLAGS=-Werror CC=clang-10 CXX=clang++-10  meson -Dtests=unsafe -Dslow-tests=true -Dfuzz-tests=true --werror --optimization=3 -Db_lto=true build
ninja -C ./build

I’ve opened https://github.com/systemd/systemd/pull/18590 to “fix” it.