Add a set of tests to ensure that the cbor.h remains C90-compatible

Signed-off-by: Thiago Macieira <thiago.macieira@intel.com>

tests/c90/c90.pro

@@ -0,0 +1,6 @@
+CONFIG += testcase parallel_test
+CONFIG -= qt
+gcc: QMAKE_CFLAGS += -std=c90 -pedantic-errors -Wall -Wextra -Werror
+
+SOURCES += tst_c90.c
+INCLUDEPATH += ../../src

tests/c90/tst_c90.c

@@ -0,0 +1,30 @@
+/****************************************************************************
+**
+** Copyright (C) 2018 Intel Corporation
+**
+** Permission is hereby granted, free of charge, to any person obtaining a copy
+** of this software and associated documentation files (the "Software"), to deal
+** in the Software without restriction, including without limitation the rights
+** to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+** copies of the Software, and to permit persons to whom the Software is
+** furnished to do so, subject to the following conditions:
+**
+** The above copyright notice and this permission notice shall be included in
+** all copies or substantial portions of the Software.
+**
+** THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+** IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+** FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+** AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+** LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+** OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+** THE SOFTWARE.
+**
+****************************************************************************/
+
+#include "cbor.h"
+
+int main()
+{
+    return 0;
+}