Enable TLS descriptors on x86-64 (GCC only)

Part of: <https://fedoraproject.org/wiki/Changes/GNUToolchainF40>

buildflags.md

@@ -622,6 +622,8 @@ tuning in the `gcc` package.  These settings are:
    applied.  The default can be overriden (for any distribution)
    by specifying `--target x86_64_v2`, `--target x86_64_v3`,
    `--target x86_64_v4` in the `rpmbuild` invocation.
+   With the GCC toolchain, TLS descriptors are enabled using
+   `-mtls-dialect=gnu2`.
 * **aarch64** does not have any architecture-specific tuning.
 
 ### Vala-specific compiler flags

macros

@@ -148,7 +148,8 @@ for k,_ in pairs(stripped_flags) do print(k .. " ") end
 %__cflags_arch_x86_64_level %[0%{?rhel} == 9 ? "-v2" : ""]%[0%{?rhel} > 9 ? "-v3" : ""]
 %__cflags_arch_x86_64 -march=x86-64%{?__cflags_arch_x86_64_level:%{__cflags_arch_x86_64_level}}
 
-%__cflags_arch_x86_64_common -mtune=generic -fasynchronous-unwind-tables -fstack-clash-protection -fcf-protection %{_frame_pointers_cflags} %{_frame_pointers_cflags_x86_64}
+# -mtls-dialect=gnu2 is currently specific to GCC (#2263181).
+%__cflags_arch_x86_64_common -mtune=generic -fasynchronous-unwind-tables -fstack-clash-protection -fcf-protection %[ "%{toolchain}" == "gcc" ? "-mtls-dialect=gnu2 " : "" ]%{_frame_pointers_cflags} %{_frame_pointers_cflags_x86_64}
 
 # Also used for s390.
 %__cflags_arch_s390x %[0%{?rhel} >= 9 ? "-march=z14 -mtune=z15" : "-march=z13 -mtune=z14"]

redhat-rpm-config.spec

@@ -4,7 +4,7 @@
 # 2) When making changes, increment the version (in baserelease) by 1.
 #    rpmdev-bumpspec and other tools update the macro below, which is used
 #    in Version: to get the desired effect.
-%global baserelease 286
+%global baserelease 287
 
 Summary: Red Hat specific rpm configuration files
 Name: redhat-rpm-config
@@ -262,6 +262,9 @@ install -p -m 644 -t %{buildroot}%{_rpmluadir}/fedora common.lua
 %doc buildflags.md
 
 %changelog
+* Thu Mar 14 2024 Florian Weimer <fweimer@redhat.com> - 287-1
+- Enable TLS descriptors on x86-64 (GCC only)
+
 * Tue Mar 12 2024 Omair Majid <omajid@redhat.com> - 286-1
 - Define %%dotnet_arches with a list of .NET-compatible architectures