1. "pcre" stands for "Perl Compatible Regular Expressions".
You can find out more information from their web page, http://www.pcre.org:
The PCRE library is a set of functions that implement regular expression pattern matching using the same syntax and semantics as Perl 5. PCRE has its own native API, as well as a set of wrapper functions that correspond to the POSIX regular expression API. The PCRE library is free, even for building commercial software.
2. You will probably also find out that pcre is not a "GCC library". It is, however, a library that may be used with the Gcc compiler.