Build: Enable ninja-based builds

This commit enables to use of `-GNinja` for builds, which
provides significantly faster TF-M builds, and enables
building TF-M as a cmake external project with Zephyr's
build system.

```
$ cmake -GNinja \
  -DPROJ_CONFIG=`readlink -f ../configs/ConfigDefault.cmake` \
  -DTARGET_PLATFORM=LPC55S69 -DBL2=False -DCOMPILER=GNUARM ..
$ ninja
```

Signed-off-by: Kevin Townsend <kevin.townsend@linaro.org>
Change-Id: I5deaaf9ffb3ec3329174881d70fe7033b531ec49
diff --git a/BuildMbedCrypto.cmake b/BuildMbedCrypto.cmake
index 4d5caee..e697111 100644
--- a/BuildMbedCrypto.cmake
+++ b/BuildMbedCrypto.cmake
@@ -109,6 +109,7 @@
 #this target installation happens only when a clean mbed-crypto build is executed.
 add_custom_target(${MBEDCRYPTO_TARGET_NAME}_install
     COMMAND ${CMAKE_COMMAND} --build ${MBEDCRYPTO_BINARY_DIR}  -- install
+    BYPRODUCTS ${MBEDCRYPTO_INSTALL_DIR}/lib/${CMAKE_STATIC_LIBRARY_PREFIX_C}mbedcrypto${CMAKE_STATIC_LIBRARY_SUFFIX_C}
     WORKING_DIRECTORY ${MBEDCRYPTO_BINARY_DIR}
     COMMENT "Installing Mbed Crypto to ${MBEDCRYPTO_INSTALL_DIR}"
     VERBATIM)