[libc] disable printf Lf tests for float128 plats

[michaelrj]

Summary

The results for the %Lf tests were calculated on 80 bit long double
systems, meaning the results are not necessarily accurate for float128
systems. In future these will be fixed, but for the moment I'm just
turning them off.

libc/test/src/stdio/sprintf_test.cpp

TEST_F(LlvmLibcSPrintfTest, FloatDecimalConv) {
   written = __llvm_libc::sprintf(buff, "%f", nan);
   ASSERT_STREQ_LEN(written, buff, "nan");
 
   written = __llvm_libc::sprintf(buff, "%F", -nan);
   ASSERT_STREQ_LEN(written, buff, "-NAN");
 
   // Length Modifier Tests.
 
-  // TODO: Fix long doubles (needs bigger table or alternate algorithm.)
-  // Currently the table values are generated, which is very slow.
+  // TODO(michaelrj): Add tests for LONG_DOUBLE_IS_DOUBLE and 128 bit long
+  // double systems.
+  // TODO(michaelrj): Fix the tests to only depend on the digits the long double
+  // is accurate for.
 
   written = __llvm_libc::sprintf(buff, "%Lf", 1.0L);
   ASSERT_STREQ_LEN(written, buff, "1.000000");
 
+#if defined(SPECIAL_X86_LONG_DOUBLE)
+
   written = __llvm_libc::sprintf(buff, "%Lf", 1e100L);
   ASSERT_STREQ_LEN(written, buff,
                    "99999999999999999996693535322073426194986990198284960792713"
                    "91541752018669482644324418977840117055488.000000");
 
   char big_buff[10000];
 
-  // written = __llvm_libc::sprintf(big_buff, "%Lf", 0x1p16383L);
-
   written = __llvm_libc::sprintf(big_buff, "%Lf", 1e1000L);
   ASSERT_STREQ_LEN(
       written, big_buff,
       "999999999999999999973107317669562353428234857594552594925899449376328728"
       "202461036775511405481186963193066642191664822065529414252060696836533522"
       "387143501724276282079456797058697369889056407118642873669166717313763499"
       "277025985141177344925615052465165938514140943010597323750202561187880136"
       "174810574553749194614479541820148407958204853833697063267336294787191005"
ASSERT_STREQ_LEN(
       "708108432086217134763779632408473684293543722127232658767439906910370146"
       "716836295909075482355827087389127370874842532825987593970846704144140471"
       "956027276735614286138656432085771988513977140957180090146798065497158947"
       "229765733489703157617307078835099906185890777007500964162371428641176460"
       "739074789794941408428328217107759915202650066155868439585510978709442590"
       "231934194956788626761834746430104077432547436359522462253411168467463134"
       "24896.000000");
 
-
   written = __llvm_libc::sprintf(big_buff, "%.10Lf", 1e-10L);
-  ASSERT_STREQ_LEN(
-      written, big_buff, "0.0000000001");
+  ASSERT_STREQ_LEN(written, big_buff, "0.0000000001");
 
   written = __llvm_libc::sprintf(big_buff, "%.7500Lf", 1e-4900L);
   ASSERT_STREQ_LEN(
       written, big_buff,
       "0."
       "000000000000000000000000000000000000000000000000000000000000000000000000"
       "000000000000000000000000000000000000000000000000000000000000000000000000"
       "000000000000000000000000000000000000000000000000000000000000000000000000"
ASSERT_STREQ_LEN(
       "249667793845728355381309084891765979111348980470647082269921872595470473"
       "719354467594516320911964549508538492057120740224559944452120552719041944"
       "961475548547884309626382512432626380881023756568143060204097921571153170"
       "723817845809196253498326358439807445210362177680590181657555380795450462"
       "223805222580359379367452693270553602179122419370586308101820559214330382"
       "570449525088342437216896462077260223998756027453411520977536701491759878"
       "422771447006016890777855573925295187921971811871399320142563330377888532"
       "179817332113");
+#endif // SPECIAL_X86_LONG_DOUBLE
 
   /*
     written = __llvm_libc::sprintf(buff, "%La", 0.1L);
   #if defined(SPECIAL_X86_LONG_DOUBLE)
     ASSERT_STREQ_LEN(written, buff, "0xc.ccccccccccccccdp-7");
   #elif defined(LONG_DOUBLE_IS_DOUBLE)
     ASSERT_STREQ_LEN(written, buff, "0x1.999999999999ap-4");
   #else // 128 bit long double