shared/libcrypt-util: use libcrypt_ra()

shared/libcrypt-util: use libcrypt_ra()

This lets the libc/xcrypt allocate as much storage area as it needs.
Should fix #16965:

testsuite-46.sh[74]: ==74==ERROR: AddressSanitizer: stack-buffer-overflow on address 0x7f3e972e1080 at pc 0x7f3e9be8deed bp 0x7ffce4f28530 sp 0x7ffce4f27ce0
testsuite-46.sh[74]: WRITE of size 131232 at 0x7f3e972e1080 thread T0
testsuite-46.sh[74]:     #0 0x7f3e9be8deec  (/usr/lib/clang/10.0.1/lib/linux/libclang_rt.asan-x86_64.so+0x9feec)
testsuite-46.sh[74]:     #1 0x559cd05a6412 in user_record_make_hashed_password /systemd-meson-build/../build/src/home/user-record-util.c:818:21
testsuite-46.sh[74]:     #2 0x559cd058fb03 in create_home /systemd-meson-build/../build/src/home/homectl.c:1112:29
testsuite-46.sh[74]:     #3 0x7f3e9b5b3058 in dispatch_verb /systemd-meson-build/../build/src/shared/verbs.c:103:24
testsuite-46.sh[74]:     #4 0x559cd058c101 in run /systemd-meson-build/../build/src/home/homectl.c:3325:16
testsuite-46.sh[74]:     #5 0x559cd058c00a in main /systemd-meson-build/../build/src/home/homectl.c:3328:1
testsuite-46.sh[74]:     #6 0x7f3e9a88b151 in __libc_start_main (/usr/lib/libc.so.6+0x28151)
testsuite-46.sh[74]:     #7 0x559cd0583e7d in _start (/usr/bin/homectl+0x24e7d)
testsuite-46.sh[74]: Address 0x7f3e972e1080 is located in stack of thread T0 at offset 32896 in frame
testsuite-46.sh[74]:     #0 0x559cd05a60df in user_record_make_hashed_password /systemd-meson-build/../build/src/home/user-record-util.c:789
testsuite-46.sh[74]:   This frame has 6 object(s):
testsuite-46.sh[74]:     [32, 40) 'priv' (line 790)
testsuite-46.sh[74]:     [64, 72) 'np' (line 791)
testsuite-46.sh[74]:     [96, 104) 'salt' (line 809)
testsuite-46.sh[74]:     [128, 32896) 'cd' (line 810)
testsuite-46.sh[74]:     [33152, 33168) '.compoundliteral' <== Memory access at offset 32896 partially underflows this variable
testsuite-46.sh[74]:     [33184, 33192) 'new_array' (line 832) <== Memory access at offset 32896 partially underflows this variable
testsuite-46.sh[74]: HINT: this may be a false positive if your program uses some custom stack unwind mechanism, swapcontext or vfork
testsuite-46.sh[74]:       (longjmp and C++ exceptions *are* supported)
testsuite-46.sh[74]: SUMMARY: AddressSanitizer: stack-buffer-overflow (/usr/lib/clang/10.0.1/lib/linux/libclang_rt.asan-x86_64.so+0x9feec)

It seems 'struct crypt_data' is 32896 bytes, but libclang_rt wants more, at least 33168?