Use $PWD instead of $(pwd) for consistency

Change the new baremetal all.sh tests to use $PWD rather than
calling pwd again directly.

Signed-off-by: David Horstmann <david.horstmann@arm.com>
diff --git a/tests/scripts/all.sh b/tests/scripts/all.sh
index 01c369a..8a690cd 100755
--- a/tests/scripts/all.sh
+++ b/tests/scripts/all.sh
@@ -1435,7 +1435,7 @@
 component_build_crypto_baremetal () {
   msg "build: make, crypto only, baremetal config"
   scripts/config.py crypto_baremetal
-  make CFLAGS="-O1 -Werror -I$(pwd)/tests/include/baremetal-override/"
+  make CFLAGS="-O1 -Werror -I$PWD/tests/include/baremetal-override/"
   are_empty_libraries library/libmbedx509.* library/libmbedtls.*
 }
 support_build_crypto_baremetal () {
@@ -1445,7 +1445,7 @@
 component_build_baremetal () {
   msg "build: make, baremetal config"
   scripts/config.py baremetal
-  make CFLAGS="-O1 -Werror -I$(pwd)/tests/include/baremetal-override/"
+  make CFLAGS="-O1 -Werror -I$PWD/tests/include/baremetal-override/"
 }
 support_build_baremetal () {
     # Older Glibc versions include time.h from other headers such as stdlib.h,