Avoid using GNU extensions in the dependency splitter regex

Sticking to POSIX-compatible extended regular expressions makes the code
more portable.  In particular, this change is required to avoid an abort
at load time on FreeBSD.

No functional change intended.

libdnf/repo/DependencySplitter.cpp

@@ -29,7 +29,7 @@
 namespace libdnf {
 
 static const Regex RELDEP_REGEX = 
-    Regex("^(\\S*)\\s*(<=|>=|<|>|=|==)?\\s*(\\S*)$", REG_EXTENDED);
+    Regex("^([^[:space:]]*)[[:space:]]*(<=|>=|<|>|=|==)?[[:space:]]*([^[:space:]]*)$", REG_EXTENDED);
 
 static bool
 getCmpFlags(int *cmp_type, std::string matchCmpType)