The recent summary of Kernel 4.15 mentioned the test for ‘compliant’ versions of GCC which fully support the retpoline mitigation, but only gave an example of non-compliance:

With GCC 7.2:

~]$ cat /sys/devices/system/cpu/vulnerabilities/spectre_v2
 Vulnerable: Minimal generic ASM retpoline

I re-created Fedora (Rawhide) GCC 7.3.1 for Fedora 27, and it gives the following, after Kernel 4.15 compilation/boot:

~]$ cat /sys/devices/system/cpu/vulnerabilities/spectre_v2
 Mitigation: Full generic retpoline

GCC 7.3.x should be available for Fedora 27 and other Distros, soon..

Robert Gadsdon.  February 1, 2018.