curl: fix build when proxy is not enabled in PACKAGECONFIG
Backport upstream patches to fix issues introduced by a backported CVE
patch. Fixes:
| ../../curl-7.75.0/lib/vtls/vtls.c: In function ‘Curl_ssl_addsessionid’:
| ../../curl-7.75.0/lib/vtls/vtls.c:508:14: error: ‘isProxy’ redeclared as different kind of symbol
| 508 | const bool isProxy = FALSE;
| | ^~~~~~~
| ../../curl-7.75.0/lib/vtls/vtls.c:488:37: note: previous definition of ‘isProxy’ with type ‘_Bool’
| 488 | bool isProxy,
| | ^
