eclair/build-tfa.sh: Explicitly remove build dir before each build

E.g., there're seen issues to build juno 64-bit after juno 32-bit.

Signed-off-by: Paul Sokolovsky <paul.sokolovsky@linaro.org>
Change-Id: If9026257ae3b6ee811807561dc8c697ba6810a60
diff --git a/eclair/build-tfa.sh b/eclair/build-tfa.sh
index 0a5a696..ae2380e 100755
--- a/eclair/build-tfa.sh
+++ b/eclair/build-tfa.sh
@@ -12,6 +12,10 @@
 env
 
 cd ${WORKSPACE}/trusted-firmware-a
+# "make clean" seems to may leave some traces from previous builds, so start
+# with removing the build dir. Still issue make clean, as it's best practice
+# (for ECLAIR processing too).
+rm -rf build/
 make clean DEBUG=${DEBUG}
 
 # Replace '$(PWD)' with the *current* $PWD.