gh-89640: Restore configure error message on failure to detect float word order (#126569)

Before #126387, if we didn't detect float word order we'd raise the following
configure error:

    Unknown float word ordering. You need to manually preset
    ax_cv_c_float_words_bigendian=no (or yes) according to your system.

This puts it back (except for ARM or WASM, which as hardcoded).

2 files changed, 7 insertions, 2 deletions

diff --git a/configure b/configure
index 71ffe9c..7a9d962 100755
--- a/configure
+++ b/configure
@@ -24219,7 +24219,7 @@ printf "%s\n" "#define DOUBLE_IS_ARM_MIXED_ENDIAN_IEEE754 1" >>confdefs.h
 printf "%s\n" "#define DOUBLE_IS_LITTLE_ENDIAN_IEEE754 1" >>confdefs.h
  ;; #(
   *) :
-     ;;
+    as_fn_error $? "Unknown float word ordering. You need to manually preset ax_cv_c_float_words_bigendian=no (or yes) according to your system." "$LINENO" 5 ;;
 esac ;;
 esac
 
diff --git a/configure.ac b/configure.ac
index 36199b3..bc3d2d0 100644
--- a/configure.ac
+++ b/configure.ac
@@ -5920,7 +5920,12 @@ AX_C_FLOAT_WORDS_BIGENDIAN(
                                 stored in ARM mixed-endian order (byte order 45670123)])],
            [wasm*], [AC_DEFINE([DOUBLE_IS_LITTLE_ENDIAN_IEEE754], [1],
                                [Define if C doubles are 64-bit IEEE 754 binary format,
-                                stored with the least significant byte first])])])
+                                stored with the least significant byte first])],
+           [AC_MSG_ERROR([m4_normalize([
+             Unknown float word ordering. You need to manually
+             preset ax_cv_c_float_words_bigendian=no (or yes)
+             according to your system.
+           ])])])])
 
 # The short float repr introduced in Python 3.1 requires the
 # correctly-rounded string <-> double conversion functions from