Fix: Stop opteesp environment using default libc

The opteesp environment uses the libc implementation part of the
SPDEV-KIT. Projects targeting the opteesp environment shall be
configured to stop using the standard library and its header files
part of the compiler package.
This patch:
  - adds the missing compiler and linker options
  - adds header files missing from SPDEV-KITs libc implementation
  - extends the external component cmake files to align build options
    with the main project
  - moves environment specific mandatory flags to a common file
  - fixes the supported C standard from gnuc99 to c99

The following files where forked from TF-A
 (https://git.trustedfirmware.org/TF-A/trusted-firmware-a.git; SHA: 7737fdf0ed):
- stdarg.h
- stdbool.h
- stddef.h
- stddef_.h

Signed-off-by: Andrew Beggs <andrew.beggs@arm.com>
Signed-off-by: Gyorgy Szing <Gyorgy.Szing@arm.com>
Change-Id: I3890453a29b003c60c8f44dfd19d553e96b1796c
diff --git a/environments/opteesp/component.cmake b/environments/opteesp/component.cmake
index d840249..f7e391f 100644
--- a/environments/opteesp/component.cmake
+++ b/environments/opteesp/component.cmake
@@ -1,5 +1,5 @@
 #-------------------------------------------------------------------------------
-# Copyright (c) 2020, Arm Limited and Contributors. All rights reserved.
+# Copyright (c) 2020-2021, Arm Limited and Contributors. All rights reserved.
 #
 # SPDX-License-Identifier: BSD-3-Clause
 #
@@ -12,3 +12,8 @@
 target_sources(${TGT} PRIVATE
 	"${CMAKE_CURRENT_LIST_DIR}/libsp_entry.c"
 	)
+
+target_include_directories(${TGT}
+         PUBLIC
+                "${CMAKE_CURRENT_LIST_DIR}/include"
+        )