Revert "[libc][math][c23] Temporarily disable asinpif16 C23 math function" (#150755)

Reverts #150754

I should have reverted the asinpif16 PR instead of just disabling the
entrypoints.

Author: overmighty

libc/config/linux/aarch64/entrypoints.txt

@@ -660,8 +660,7 @@ if(LIBC_TYPES_HAS_FLOAT16)
   list(APPEND TARGET_LIBM_ENTRYPOINTS
     # math.h C23 _Float16 entrypoints
     # libc.src.math.acoshf16
-    # Temporarily disabled due to mpfr_asinpi requiring MPFR >= 4.2.0.
-    # libc.src.math.asinpif16
+    libc.src.math.asinpif16
     libc.src.math.canonicalizef16
     libc.src.math.ceilf16
     libc.src.math.copysignf16

libc/config/linux/x86_64/entrypoints.txt

@@ -703,8 +703,7 @@ if(LIBC_TYPES_HAS_FLOAT16)
     libc.src.math.acospif16
     libc.src.math.asinf16
     libc.src.math.asinhf16
-    # Temporarily disabled due to mpfr_asinpi requiring MPFR >= 4.2.0.
-    # libc.src.math.asinpif16
+    libc.src.math.asinpif16
     libc.src.math.atanf16
     libc.src.math.atanhf16
     libc.src.math.canonicalizef16