Add a test component with malloc(0) returning NULL

Exercise the library functions with calloc returning NULL for a size
of 0. Make this a separate job with UBSan (and ASan) to detect
places where we try to dereference the result of calloc(0) or to do
things like

    buf = calloc(size, 1);
    if (buf == NULL && size != 0) return INSUFFICIENT_MEMORY;
    memcpy(buf, source, size);

which has undefined behavior when buf is NULL at the memcpy call even
if size is 0.

This is needed because other test components jobs either use the system
malloc which returns non-NULL on Linux and FreeBSD, or the
memory_buffer_alloc malloc which returns NULL but does not give as
useful feedback with ASan (because the whole heap is a single C
object).

tests/scripts/all.sh

@@ -822,6 +822,21 @@ component_test_platform_calloc_macro () {
     make test
 }
 
+component_test_malloc_0_null () {
+    msg "build: malloc(0) returns NULL (ASan+UBSan build)"
+    scripts/config.pl full
+    scripts/config.pl unset MBEDTLS_MEMORY_BUFFER_ALLOC_C
+    make CC=gcc CFLAGS="'-DMBEDTLS_CONFIG_FILE=\"$PWD/tests/configs/config-wrapper-malloc-0-null.h\"' -O -Werror -Wall -Wextra -fsanitize=address,undefined" LDFLAGS='-fsanitize=address,undefined'
+
+    msg "test: malloc(0) returns NULL (ASan+UBSan build)"
+    make test
+
+    msg "selftest: malloc(0) returns NULL (ASan+UBSan build)"
+    # Just the calloc selftest. "make test" ran the others as part of the
+    # test suites.
+    if_build_succeeded programs/test/selftest calloc
+}
+
 component_test_aes_fewer_tables () {
     msg "build: default config with AES_FEWER_TABLES enabled"
     scripts/config.pl set MBEDTLS_AES_FEWER_TABLES