Fix MBEDTLS_NO_PLATFORM_ENTROPY for baremetal aarch64 with armclang

Signed-off-by: Dave Rodgman <dave.rodgman@arm.com>
diff --git a/configs/config-tfm.h b/configs/config-tfm.h
index 197b808..8ed0792 100644
--- a/configs/config-tfm.h
+++ b/configs/config-tfm.h
@@ -21,9 +21,6 @@
 /* MBEDTLS_PSA_CRYPTO_SPM needs third-party files, so disable it. */
 #undef MBEDTLS_PSA_CRYPTO_SPM
 
-/* Use built-in platform entropy functions (TF-M provides its own). */
-#undef MBEDTLS_NO_PLATFORM_ENTROPY
-
 /* Disable buffer-based memory allocator. This isn't strictly required,
  * but using the native allocator is faster and works better with
  * memory management analysis frameworks such as ASan. */
@@ -53,10 +50,14 @@
 /*
  * In order to get an example config that works cleanly out-of-the-box
  * for both baremetal and non-baremetal builds, we detect baremetal builds
- * and set this variable automatically.
+ * (either IAR, Arm compiler or __ARM_EABI__ defined), and adjust some
+ * variables accordingly.
  */
-#if defined(__IAR_SYSTEMS_ICC__) || defined(__ARM_EABI__)
+#if defined(__IAR_SYSTEMS_ICC__) || defined(__ARMCC_VERSION) || defined(__ARM_EABI__)
 #define MBEDTLS_NO_PLATFORM_ENTROPY
+#else
+/* Use built-in platform entropy functions (TF-M provides its own). */
+#undef MBEDTLS_NO_PLATFORM_ENTROPY
 #endif
 
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