[gdb/testsuite] Fix gdb.ada/fixed_points.exp for gcc < 10

[gdb/testsuite] Fix gdb.ada/fixed_points.exp for gcc < 10

When running test-case gdb.ada/fixed_points.exp with system gcc 7, I run
into:
...
(gdb) PASS: gdb.ada/fixed_points.exp: scenario=all: print fp4_var / 1
get_compiler_info: gcc-7-5-0
p Float(Another_Fixed) = Float(Another_Delta * 5)^M
No definition of "another_delta" in current context.^M
(gdb) FAIL: gdb.ada/fixed_points.exp: scenario=all: value of another_fixed
...

This is a regression since commit 1411185a57e ("Introduce and use
gnat_version_compare"), which did:
...
     # This failed before GCC 10.
-    if {$scenario == "all" && [test_compiler_info {gcc-10-*}]} {
+    if {$scenario == "all" && [gnat_version_compare < 10]} {
 	gdb_test "p Float(Another_Fixed) = Float(Another_Delta * 5)" "true" \
 	    "value of another_fixed"
     }
...

Fix this by using gnat_version_compare >= 10 instead.

Tested on x86_64-linux, with gcc 7 - 13.