Fix buildinf.h generation for space and backslash

Fix buildinf.h generation for space and backslash

Builds may be configured with CC or CFLAGS containing space and
double quotes. In particular on Windows, this may lead to passing
more than two arguments into mkbuildinf.pl.
In addition, backslashes must be escaped for constructing the C string.

Fixes #26253.

Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Richard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/26315)