libm/libm: Do not force type size evaluation.

Since C99, `FLT_EVAL_METHOD` should be left for the compiler/libc to
define.

This also breaks compilation with picolibc as the target's libc, since
it defines said symbol in math.h before the libm define is evaluated by
the compiler.

Signed-off-by: Alessandro Gatti <a.gatti@frob.it>

lib/libm/libm.h

@@ -19,8 +19,6 @@
 #include <stdint.h>
 #include <math.h>
 
-#define FLT_EVAL_METHOD 0
-
 #define FORCE_EVAL(x) do {                        \
 	if (sizeof(x) == sizeof(float)) {         \
 		volatile float __x;               \

lib/libm_dbl/libm.h

@@ -15,8 +15,6 @@
 #include <stdint.h>
 #include <math.h>
 
-#define FLT_EVAL_METHOD 0
-
 #define FORCE_EVAL(x) do {                        \
 	if (sizeof(x) == sizeof(float)) {         \
 		volatile float __x;               \