build: silence mingw32ce C99 format warnings, simplify CI

[vszakats]

./configure mingw32ce builds enable C99 mode automatically, that
triggers compiler warnings in gcc 4.4.0. We initially worked it around
in CI by suppressing the detection of C99 with ac_cv_prog_cc_c99=no.

Replace it with automatically silencing the bogus warnings in C99 mode,
for all build systems:

lib/ftp.c: In function 'Curl_GetFTPResponse':
lib/ftp.c:726: error: format '%zd' expects type 'signed size_t', but argument 4 has type 'ssize_t'
lib/ws.c: In function 'ws_dec_pass_payload':
lib/ws.c:304: error: format '%zd' expects type 'signed size_t', but argument 3 has type 'ssize_t'
lib/ws.c: In function 'ws_enc_write_head':
lib/ws.c:581: error: format '%zd' expects type 'signed size_t', but argument 3 has type 'long int'
lib/vtls/schannel.c: In function 'schannel_connect_step1':
lib/vtls/schannel.c:1122: error: format '%zd' expects type 'signed size_t', but argument 3 has type 'ssize_t'
lib/vtls/schannel.c: In function 'schannel_connect_step2':
lib/vtls/schannel.c:1311: error: format '%zd' expects type 'signed size_t', but argument 3 has type 'ssize_t'
lib/vtls/schannel.c: In function 'schannel_send':
lib/vtls/schannel.c:1793: error: format '%zd' expects type 'signed size_t', but argument 3 has type 'ssize_t'
lib/vtls/schannel.c:1810: error: format '%zd' expects type 'signed size_t', but argument 3 has type 'ssize_t'
lib/vtls/schannel.c: In function 'schannel_shutdown':                         
lib/vtls/schannel.c:2286: error: format '%zd' expects type 'signed size_t', but argument 4 has type 'ssize_t'
lib/vtls/vtls.c: In function 'ssl_cf_recv':                                   
lib/vtls/vtls.c:1422: error: format '%zd' expects type 'signed size_t', but argument 5 has type 'ssize_t'

Ref: https://github.com/curl/curl/actions/runs/13533841306/job/37821720902?pr=16492#step:9:20

Also: simplify Windows CE job configuration in GHA/windows.

Follow-up to 2a292c3 #15975

[vszakats]

After silencing the bogus WinCE warnings, the next question is why does autotools want to detect C11 and C99 in these builds, and not in others:

checking whether /Users/runner/opt/mingw32ce/bin/arm-mingw32ce-gcc accepts -g... yes
checking for /Users/runner/opt/mingw32ce/bin/arm-mingw32ce-gcc option to enable C11 features... unsupported
checking for /Users/runner/opt/mingw32ce/bin/arm-mingw32ce-gcc option to enable C99 features... -std=gnu99
checking whether /Users/runner/opt/mingw32ce/bin/arm-mingw32ce-gcc -std=gnu99 understands -c and -o together... yes

https://github.com/curl/curl/actions/runs/13534146058/job/37822577315?pr=16492#step:6:74

vs. a normal mingw builds:

checking whether gcc accepts -g... yes
checking for gcc option to enable C11 features... none needed
checking whether gcc understands -c and -o together... yes

https://github.com/curl/curl/actions/runs/13534146058/job/37822579122?pr=16492#step:7:73

[jay]

After silencing the bogus WinCE warnings, the next question is why does autotools want to detect C11 and C99 in these builds, and not in others

There's probably something legacy in the compiler that it detects (or, can't detect..) and so it needs to interrogate more than usual. I wouldn't sweat it.