build: reorder cxxflags in intrinsic checks

Let the user have the final say in regards to using intrinsics.

Fixes: bitcoin#13758
Alternaitve to bitcoin#13789.

configure.ac

@@ -518,7 +518,7 @@ if test "$enable_clmul" = "yes"; then
 fi
 
 TEMP_CXXFLAGS="$CXXFLAGS"
-CXXFLAGS="$CXXFLAGS $SSE42_CXXFLAGS"
+CXXFLAGS="$SSE42_CXXFLAGS $CXXFLAGS"
 AC_MSG_CHECKING([for SSE4.2 intrinsics])
 AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[
     #include <stdint.h>
@@ -540,7 +540,7 @@ AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[
 CXXFLAGS="$TEMP_CXXFLAGS"
 
 TEMP_CXXFLAGS="$CXXFLAGS"
-CXXFLAGS="$CXXFLAGS $SSE41_CXXFLAGS"
+CXXFLAGS="$SSE41_CXXFLAGS $CXXFLAGS"
 AC_MSG_CHECKING([for SSE4.1 intrinsics])
 AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[
     #include <stdint.h>
@@ -555,7 +555,7 @@ AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[
 CXXFLAGS="$TEMP_CXXFLAGS"
 
 TEMP_CXXFLAGS="$CXXFLAGS"
-CXXFLAGS="$CXXFLAGS $AVX2_CXXFLAGS"
+CXXFLAGS="$AVX2_CXXFLAGS $CXXFLAGS"
 AC_MSG_CHECKING([for AVX2 intrinsics])
 AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[
     #include <stdint.h>
@@ -570,7 +570,7 @@ AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[
 CXXFLAGS="$TEMP_CXXFLAGS"
 
 TEMP_CXXFLAGS="$CXXFLAGS"
-CXXFLAGS="$CXXFLAGS $X86_SHANI_CXXFLAGS"
+CXXFLAGS="$X86_SHANI_CXXFLAGS $CXXFLAGS"
 AC_MSG_CHECKING([for x86 SHA-NI intrinsics])
 AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[
     #include <stdint.h>
@@ -591,7 +591,7 @@ AX_CHECK_COMPILE_FLAG([-march=armv8-a+crc+crypto], [ARM_CRC_CXXFLAGS="-march=arm
 AX_CHECK_COMPILE_FLAG([-march=armv8-a+crc+crypto], [ARM_SHANI_CXXFLAGS="-march=armv8-a+crc+crypto"], [], [$CXXFLAG_WERROR])
 
 TEMP_CXXFLAGS="$CXXFLAGS"
-CXXFLAGS="$CXXFLAGS $ARM_CRC_CXXFLAGS"
+CXXFLAGS="$ARM_CRC_CXXFLAGS $CXXFLAGS"
 AC_MSG_CHECKING([for ARMv8 CRC32 intrinsics])
 AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[
     #include <arm_acle.h>
@@ -610,7 +610,7 @@ AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[
 CXXFLAGS="$TEMP_CXXFLAGS"
 
 TEMP_CXXFLAGS="$CXXFLAGS"
-CXXFLAGS="$CXXFLAGS $ARM_SHANI_CXXFLAGS"
+CXXFLAGS="$ARM_SHANI_CXXFLAGS $CXXFLAGS"
 AC_MSG_CHECKING([for ARMv8 SHA-NI intrinsics])
 AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[
     #include <arm_acle.h>