Build: Add MBEDTLS_TARGET_PREFIX

Allows required targets to have prefixes added to them, so that external
projects can avoid target names clashing.

Signed-off-by: Raef Coles <raef.coles@arm.com>
diff --git a/programs/test/CMakeLists.txt b/programs/test/CMakeLists.txt
index 0df0bec..217741b 100644
--- a/programs/test/CMakeLists.txt
+++ b/programs/test/CMakeLists.txt
@@ -1,5 +1,5 @@
 set(libs
-    mbedtls
+    ${mbedtls_target}
 )
 
 if(USE_PKCS11_HELPER_LIBRARY)
@@ -33,7 +33,7 @@
     if (${exe_index} GREATER -1)
         target_link_libraries(${exe} ${libs})
     else()
-        target_link_libraries(${exe} mbedcrypto)
+        target_link_libraries(${exe} ${mbedcrypto_target})
     endif()
 endforeach()
 
diff --git a/programs/test/cmake_subproject/CMakeLists.txt b/programs/test/cmake_subproject/CMakeLists.txt
index 3e32c5f..a9fcfde 100644
--- a/programs/test/cmake_subproject/CMakeLists.txt
+++ b/programs/test/cmake_subproject/CMakeLists.txt
@@ -1,5 +1,8 @@
 cmake_minimum_required(VERSION 2.6)
 
+# Test the target renaming support by adding a prefix to the targets built
+set(MBEDTLS_TARGET_PREFIX subproject_test_)
+
 # We use the parent Mbed TLS directory as the MBEDTLS_DIR for this test. Other
 # projects that use Mbed TLS as a subproject are likely to add by their own
 # relative paths.
@@ -8,11 +11,12 @@
 # Add Mbed TLS as a subdirectory.
 add_subdirectory(${MBEDTLS_DIR} build)
 
-# Link against all the Mbed TLS libraries.
+# Link against all the Mbed TLS libraries. Verifies that the targets have been
+# created using the specified prefix
 set(libs
-    mbedcrypto
-    mbedx509
-    mbedtls
+    subproject_test_mbedcrypto
+    subproject_test_mbedx509
+    subproject_test_mbedtls
 )
 
 add_executable(cmake_subproject cmake_subproject.c)