Clean up constant-flow memsan testing

Disable asm in memsan constant-flow testing and adjust
test_suit_bignum_core.function accordingly

Signed-off-by: Elena Uziunaite <elena.uziunaite@arm.com>
diff --git a/tests/scripts/all.sh b/tests/scripts/all.sh
index a1203f7..3eca325 100755
--- a/tests/scripts/all.sh
+++ b/tests/scripts/all.sh
@@ -2202,6 +2202,7 @@
     scripts/config.py set MBEDTLS_TEST_CONSTANT_FLOW_MEMSAN
     scripts/config.py unset MBEDTLS_USE_PSA_CRYPTO
     scripts/config.py unset MBEDTLS_AESNI_C # memsan doesn't grok asm
+    scripts/config.py unset MBEDTLS_HAVE_ASM
     CC=clang cmake -D CMAKE_BUILD_TYPE:String=MemSan .
     make
 
@@ -2220,6 +2221,7 @@
     scripts/config.py full
     scripts/config.py set MBEDTLS_TEST_CONSTANT_FLOW_MEMSAN
     scripts/config.py unset MBEDTLS_AESNI_C # memsan doesn't grok asm
+    scripts/config.py unset MBEDTLS_HAVE_ASM
     CC=clang cmake -D CMAKE_BUILD_TYPE:String=MemSan .
     make