Fix Make issues with Everest enabled

Apply Gilles suggestion to fix the problem with make on the CI when everest is enabled, i.e. use $(THIRDPARTY_DIR) instead of a fuzz specific hack involving $(THIRDPARTY_INCLUDES)

Signed-off-by: Paul Elliott <paul.elliott@arm.com>
diff --git a/3rdparty/everest/Makefile.inc b/3rdparty/everest/Makefile.inc
index 77a6b49..8055ce9 100644
--- a/3rdparty/everest/Makefile.inc
+++ b/3rdparty/everest/Makefile.inc
@@ -1,6 +1,6 @@
-THIRDPARTY_INCLUDES+=-I../3rdparty/everest/include -I../3rdparty/everest/include/everest -I../3rdparty/everest/include/everest/kremlib
+THIRDPARTY_INCLUDES+=-I$(THIRDPARTY_DIR)/everest/include -I$(THIRDPARTY_DIR)/everest/include/everest -I$(THIRDPARTY_DIR)/everest/include/everest/kremlib
 
 THIRDPARTY_CRYPTO_OBJECTS+= \
-	../3rdparty/everest/library/everest.o \
-	../3rdparty/everest/library/x25519.o \
-	../3rdparty/everest/library/Hacl_Curve25519_joined.o
+	$(THIRDPARTY_DIR)/everest/library/everest.o \
+	$(THIRDPARTY_DIR)/everest/library/x25519.o \
+	$(THIRDPARTY_DIR)/everest/library/Hacl_Curve25519_joined.o
diff --git a/3rdparty/p256-m/Makefile.inc b/3rdparty/p256-m/Makefile.inc
index fc8f73b..53bb55b 100644
--- a/3rdparty/p256-m/Makefile.inc
+++ b/3rdparty/p256-m/Makefile.inc
@@ -1,5 +1,5 @@
-THIRDPARTY_INCLUDES+=-I../3rdparty/p256-m/p256-m/include -I../3rdparty/p256-m/p256-m/include/p256-m -I../3rdparty/p256-m/p256-m_driver_interface
+THIRDPARTY_INCLUDES+=-I$(THIRDPARTY_DIR)/p256-m/p256-m/include -I$(THIRDPARTY_DIR)/p256-m/p256-m/include/p256-m -I$(THIRDPARTY_DIR)/p256-m/p256-m_driver_interface
 
 THIRDPARTY_CRYPTO_OBJECTS+= \
-	../3rdparty/p256-m//p256-m_driver_entrypoints.o \
-	../3rdparty/p256-m//p256-m/p256-m.o
+	$(THIRDPARTY_DIR)/p256-m//p256-m_driver_entrypoints.o \
+	$(THIRDPARTY_DIR)/p256-m//p256-m/p256-m.o
diff --git a/programs/Makefile b/programs/Makefile
index 82c8569..6baf465 100644
--- a/programs/Makefile
+++ b/programs/Makefile
@@ -114,7 +114,7 @@
 endif
 
 fuzz: ${MBEDTLS_TEST_OBJS}
-	$(MAKE) -C fuzz THIRDPARTY_INCLUDES=$(THIRDPARTY_INCLUDES)
+	$(MAKE) -C fuzz
 
 ${MBEDTLS_TEST_OBJS}:
 	$(MAKE) -C ../tests mbedtls_test