Directly include system headers

[MichaelChirico]

As flagged by clang-tidy: https://clang.llvm.org/extra/clang-tidy/checks/misc/include-cleaner.html

[spgarbet]

This one looks fairly simple. @hadley @MichaelChirico Seeking your approval for release of this patch to CRAN.

[spgarbet]

RUNIT TEST PROTOCOL -- Mon Jul 22 09:44:49 2024

---

Number of test functions: 171
Number of errors: 0
Number of failures: 0

1 Test Suite :
yaml tests - 171 test functions, 0 errors, 0 failures

[spgarbet]

Loading required package: data.table
data.table 1.15.4 using 6 threads (see ?getDTthreads). Latest news: r-datatable.com
getDTthreads(verbose=TRUE):
OpenMP version (_OPENMP) 201511
omp_get_num_procs() 12
R_DATATABLE_NUM_PROCS_PERCENT unset (default 50)
R_DATATABLE_NUM_THREADS unset
R_DATATABLE_THROTTLE unset (default 1024)
omp_get_thread_limit() 2147483647
omp_get_max_threads() 12
OMP_THREAD_LIMIT unset
OMP_NUM_THREADS unset
RestoreAfterFork true
data.table is using 6 threads with throttle==1024. See ?setDTthreads.
test.data.table() running: /home/garbetsp/R/x86_64-pc-linux-gnu-library/4.4/data.table/tests/tests.Rraw.bz2
Running test id 2243.56
Mon Jul 22 09:46:56 2024 endian==little, sizeof(long double)==16, longdouble.digits==64, sizeof(pointer)==8, TZ==unset, Sys.timezone()=='America/Menominee', Sys.getlocale()=='LC_CTYPE=en_US.UTF-8;LC_NUMERIC=C;LC_TIME=en_US.UTF-8;LC_COLLATE=en_US.UTF-8;LC_MONETARY=en_US.UTF-8;LC_MESSAGES=en_US.UTF-8;LC_PAPER=en_US.UTF-8;LC_NAME=C;LC_ADDRESS=C;LC_TELEPHONE=C;LC_MEASUREMENT=en_US.UTF-8;LC_IDENTIFICATION=C', l10n_info()=='MBCS=TRUE; UTF-8=TRUE; Latin-1=FALSE; codeset=UTF-8', getDTthreads()=='OpenMP version (_OPENMP)==201511; omp_get_num_procs()==12; R_DATATABLE_NUM_PROCS_PERCENT==unset (default 50); R_DATATABLE_NUM_THREADS==unset; R_DATATABLE_THROTTLE==unset (default 1024); omp_get_thread_limit()==2147483647; omp_get_max_threads()==12; OMP_THREAD_LIMIT==unset; OMP_NUM_THREADS==unset; RestoreAfterFork==true; data.table is using 6 threads with throttle==1024. See ?setDTthreads.', zlibVersion()==1.2.11 ZLIB_VERSION==1.2.11
10 longest running tests took 8s (44% of 18s)
ID time nTest
1: 1438 1.354 738
2: 2155 1.142 5
3: 1437 0.852 36
4: 1648 0.852 91
5: 1650 0.814 91
6: 1652 0.803 91
7: 1223 0.717 728
8: 1252 0.552 484
9: 1642 0.524 91
10: 1646 0.523 91
All 11070 tests (last 2243.56) in tests/tests.Rraw.bz2 completed ok in 20.7s elapsed (24.4s cpu)