Make:Remove calls to shell from makefiles.

As an initial stage of making Trusted Firmware build environment more
portable, we remove most uses of the $(shell ) function and replace them
with more portable make function based solutions.

Note that the setting of BUILD_STRING still uses $(shell ) since it's
not possible to reimplement this as a make function. Avoiding invocation
of this on incompatible host platforms will be implemented separately.

Change-Id: I768e2f9a265c78814a4adf2edee4cc46cda0f5b8
diff --git a/make_helpers/build_macros.mk b/make_helpers/build_macros.mk
index b22eaf9..274f365 100644
--- a/make_helpers/build_macros.mk
+++ b/make_helpers/build_macros.mk
@@ -1,5 +1,5 @@
 #
-# Copyright (c) 2015, ARM Limited and Contributors. All rights reserved.
+# Copyright (c) 2015-2016, ARM Limited and Contributors. All rights reserved.
 #
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions are met:
@@ -28,6 +28,17 @@
 # POSSIBILITY OF SUCH DAMAGE.
 #
 
+# Some utility macros for manipulating awkward (whitespace) characters.
+blank			:=
+space			:=${blank} ${blank}
+
+# A user defined function to recursively search for a filename below a directory
+#    $1 is the directory root of the recursive search (blank for current directory).
+#    $2 is the file name to search for.
+define rwildcard
+$(strip $(foreach d,$(wildcard ${1}*),$(call rwildcard,${d}/,${2}) $(filter $(subst *,%,%${2}),${d})))
+endef
+
 # This table is used in converting lower case to upper case.
 uppercase_table:=a,A b,B c,C d,D e,E f,F g,G h,H i,I j,J k,K l,L m,M n,N o,O p,P q,Q r,R s,S t,T u,U v,V w,W x,X y,Y z,Z