perl-WWW-Curl-4.17-8.fc26 fails to build in F26 because it misparses curl.h:

Found curl.h in /usr/include/curl/curl.h
Building curlopt-constants.c for your libcurl version
Building Easy.pm constants for your libcurl version
Building Share.pm constants for your libcurl version
[...]
gcc -c  -I/usr/include -D_REENTRANT -D_GNU_SOURCE -O2 -g -pipe -Wall -Werror=format-security -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector-strong --param=ssp-buffer-size=4 -grecord-gcc-switches -m32 -march=i686 -mtune=atom -fasynchronous-unwind-tables -fwrapv -fno-strict-aliasing -I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64 -O2 -g -pipe -Wall -Werror=format-security -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector-strong --param=ssp-buffer-size=4 -grecord-gcc-switches -specs=/usr/lib/rpm/redhat/redhat-hardened-cc1 -m32 -march=i686 -mtune=atom -fasynchronous-unwind-tables   -DVERSION=\"4.17\" -DXS_VERSION=\"4.17\" -fPIC "-I/usr/lib/perl5/CORE"   Curl.c
Curl.xs: In function 'fwrite_wrapper2':
Curl.xs:363:13: warning: unused variable 'sv' [-Wunused-variable]
         SV *sv;
             ^~
In file included from Curl.xs:574:0:
curlopt-constants.c: In function 'constant':
curlopt-constants.c:19:58: warning: 'return' with no value, in function returning non-void
             if (strEQ(name, "DID_MEMORY_FUNC_TYPEDEFS")) return CURL_DID_MEMORY_FUNC_TYPEDEFS;
                                                          ^~~~~~
curlopt-constants.c:2:1: note: declared here
 constant(const char *name)
 ^~~~~~~~
curlopt-constants.c:128:49: error: 'CURL_STRICTER' undeclared (first use in this function)
             if (strEQ(name, "STRICTER")) return CURL_STRICTER;
                                                 ^~~~~~~~~~~~~

This is caused by upgrading libcurl-devel from 7.50.1-2.fc26 to 7.50.2-1.fc26 that added this into curl.h:

+#ifdef CURL_NO_OLDIES
+#define CURL_STRICTER
+#endif
+