compile time warning of 128bit ctr_drbg keys and standardized warnings

a compile time print was added warning in case of 128bit ctr_drbg keys.
This was don't to avoid an actual warning in these cases
(making build with warnings as errors possible).
Additional warnings on the Changelog/headers were set to use the same phrasing
phrasing was approved by Gilles and Janos.
diff --git a/Makefile b/Makefile
index 78c1acb..f4c0a00 100644
--- a/Makefile
+++ b/Makefile
@@ -61,9 +61,21 @@
 
 NULL_ENTROPY_WARNING=\n$(WARNING_BORDER)$(NULL_ENTROPY_WARN_L1)$(NULL_ENTROPY_WARN_L2)$(NULL_ENTROPY_WARN_L3)$(WARNING_BORDER)
 
+WARNING_BORDER_LONG      =**********************************************************************************\n
+CTR_DRBG_128_BIT_KEY_WARN_L1=****  WARNING!  MBEDTLS_CTR_DRBG_USE_128_BIT_KEY defined!                      ****\n
+CTR_DRBG_128_BIT_KEY_WARN_L2=****  Using 128-bit keys for CTR_DRBG limits the security of generated         ****\n
+CTR_DRBG_128_BIT_KEY_WARN_L3=****  keys and operations that use random values generated to 128-bit security ****\n
+
+CTR_DRBG_128_BIT_KEY_WARNING=\n$(WARNING_BORDER_LONG)$(CTR_DRBG_128_BIT_KEY_WARN_L1)$(CTR_DRBG_128_BIT_KEY_WARN_L2)$(CTR_DRBG_128_BIT_KEY_WARN_L3)$(WARNING_BORDER_LONG)
+
 # Post build steps
 post_build:
 ifndef WINDOWS
+
+	# If 128-bit keys are configured for CTR_DRBG, display an appropriate warning
+	-scripts/config.pl get MBEDTLS_CTR_DRBG_USE_128_BIT_KEY && ([ $$? -eq 0 ]) && \
+	    echo '$(CTR_DRBG_128_BIT_KEY_WARNING)'
+
 	# If NULL Entropy is configured, display an appropriate warning
 	-scripts/config.pl get MBEDTLS_TEST_NULL_ENTROPY && ([ $$? -eq 0 ]) && \
 	    echo '$(NULL_ENTROPY_WARNING)'