[libc] Move long double table option to new config (llvm#66151)

This patch adds the long double table option for printf into the new
configuration scheme. This allows it to be set for most targets but
unset for baremetal.

Author: michaelrj-google

libc/config/baremetal/config.json

@@ -8,6 +8,9 @@
     },
     "LIBC_CONF_PRINTF_DISABLE_WRITE_INT": {
       "value": true
+    },
+    "LIBC_CONF_PRINTF_FLOAT_TO_STR_USE_MEGA_LONG_DOUBLE_TABLE": {
+      "value": false
     }
   }
 }

libc/config/config.json

@@ -11,6 +11,10 @@
     "LIBC_CONF_PRINTF_DISABLE_WRITE_INT": {
       "value": false,
       "doc": "Disable handling of %n in printf format string."
+    },
+    "LIBC_CONF_PRINTF_FLOAT_TO_STR_USE_MEGA_LONG_DOUBLE_TABLE": {
+      "value": true,
+      "doc": "Use large table for better printf long double performance."
     }
   }
 }

libc/docs/configure.rst

@@ -29,3 +29,4 @@ to learn about the defaults for your platform and target.
     - ``LIBC_CONF_PRINTF_DISABLE_FLOAT``: Disable printing floating point values in printf and friends.
     - ``LIBC_CONF_PRINTF_DISABLE_INDEX_MODE``: Disable index mode in the printf format string.
     - ``LIBC_CONF_PRINTF_DISABLE_WRITE_INT``: Disable handling of %n in printf format string.
+    - ``LIBC_CONF_PRINTF_FLOAT_TO_STR_USE_MEGA_LONG_DOUBLE_TABLE``: Use large table for better printf long double performance.

libc/src/stdio/CMakeLists.txt

@@ -363,6 +363,9 @@ endif()
 if(LIBC_CONF_PRINTF_DISABLE_WRITE_INT)
   list(APPEND printf_copts "-DLIBC_COPT_PRINTF_DISABLE_WRITE_INT")
 endif()
+if(LIBC_CONF_PRINTF_FLOAT_TO_STR_USE_MEGA_LONG_DOUBLE_TABLE)
+  list(APPEND printf_copts "-DLIBC_COPT_FLOAT_TO_STR_USE_MEGA_LONG_DOUBLE_TABLE")
+endif()
 
 if(LLVM_LIBC_FULL_BUILD)
   list(APPEND printf_deps

libc/src/stdio/printf_core/CMakeLists.txt

@@ -92,7 +92,6 @@ add_object_library(
     libc.src.__support.integer_to_string
     libc.src.__support.float_to_string
   COMPILE_OPTIONS
-    -DLIBC_COPT_FLOAT_TO_STR_USE_MEGA_LONG_DOUBLE_TABLE
     ${printf_copts}
 )