btrfs-progs: ci: build static binaries on oldest supported x86-64 architecture

As mentioned on https://wiki.tnonline.net/w/Btrfs/Statically_built_btrfs-progs
the static binaries could be built on with flags so they're available on
most x86-64 models (intel, AMD).

Signed-off-by: David Sterba <dsterba@suse.com>

.github/workflows/artifacts-static-build.yml

@@ -18,9 +18,9 @@ jobs:
       - name: Configure
         run: ./autogen.sh && ./configure
       - name: Make static
-        run: make V=1 static
+        run: make V=1 EXTRA_CFLAGS='-march=x86-64' static
       - name: Make box.static
-        run: make V=1 btrfs.box.static
+        run: make V=1 EXTRA_CFLAGS='-march=x86-64' btrfs.box.static
       - name: Strip binaries
         run: strip btrfs.static btrfs.box.static
       - name: Calculate SHA256 checksums

INSTALL

@@ -92,6 +92,9 @@ of the libraries.
 The resulting binaries have the '.static' suffix, the intermediate object
 files do not conflict with the normal (dynamic) build.
 
+There are pre-built static binaries for download available at the latest
+release (under Assets), https://github.com/kdave/btrfs-progs/releases .
+
 
 All-in-one binary (busybox style)
 ---------------------------------