asm_tests: Re-optimize FYL2X for reduced precision x87 path

unittests/ASM/X87_F64/D9_F9_2_F64.asm

@@ -0,0 +1,32 @@
+%ifdef CONFIG
+{
+  "RegData": {
+    "RAX": "1"
+  },
+  "Env": { "FEX_X87REDUCEDPRECISION" : "1" }
+}
+%endif
+
+%include "checkprecision.mac"
+
+mov rsi, 0xe0000000
+
+; y=1, x = 0.25
+fld1
+lea rdx, [rel x_quarter]
+fld qword [rdx]
+fyl2xp1
+fstp qword [rsi]
+check_relerr_d rel expected_quarter, rsi, rel tolerance
+
+hlt
+
+align 8
+x_quarter:
+  dq 0x3FD0000000000000
+expected_quarter:
+  dq 0x3FD49A784BCD1B87 ; matches the LUT-based F64 FYL2X path
+tolerance:
+  dq 0x3CB0000000000000 ; 2^-52, ~1 ULP relative error
+
+define_check_data_constants