Fix #24: Add strict warning flags

Add extra compile options for mission scope and arch scope.

These are separated to support cross compile environments that
do not/cannot use the same flags on both builds.

For "mission" build the targets are never cross compiled, only
built for the native host machine.  It should be safe to assume
a compiler in the GCC family and the strict warnings should
_always_ be applicable here.

For "arch" build the options are compiler vendor dependent.  The
file as-supplied can only be used if all the target cross compilers
are in the same family and support the same warning options.
However, this file can be modified without affecting the options
used for the host side tools.

cmake/sample_defs/arch_build.cmake

@@ -0,0 +1,37 @@
+#
+# Example arch_build.cmake
+# -------------------------
+#
+# This file will be automatically included in the arch-specific build scope
+#
+# Definitions and options specified here will be used when cross-compiling 
+# _all_ FSW code for _all_ targets defined in targets.cmake.
+#
+# Avoid machine-specific code generation options in this file (e.g. -f,-m options); such 
+# options should be localized to the toolchain file such that they will only be
+# included on the machines where they apply.
+# 
+# CAUTION: In heterogeneous environments where different cross compilers are
+# used for different CPUs, particularly if from different vendors, it is likely
+# that compile options will need to be different as well.
+#
+# In general, options in this file can only be used in cases where all CPUs use a
+# compiler from the same vendor and/or are all GCC based such that they accept similar 
+# command line options.
+#
+# This file can alternatively be named as "arch_build_${TARGETSYSTEM}.cmake" 
+# where ${TARGETSYSTEM} represents the system type, matching the toolchain.
+#
+# These example options assume a GCC-style toolchain is used for cross compilation,
+# and uses the same warning options that are applied at the mission level. 
+#
+add_compile_options(
+    -std=c99                # Target the C99 standard (without gcc extensions) 
+    -pedantic               # Issue all the warnings demanded by strict ISO C
+    -Wall                   # Warn about most questionable operations
+    -Wstrict-prototypes     # Warn about missing prototypes
+    -Wwrite-strings         # Warn if not treating string literals as "const"
+    -Wpointer-arith         # Warn about suspicious pointer operations
+    -Werror                 # Treat warnings as errors (code should be clean) 
+)
+

cmake/sample_defs/mission_build.cmake

@@ -0,0 +1,27 @@
+#
+# Example mission_build.cmake
+# ---------------------------
+#
+# This file will be automatically included in the top level ("mission") build scope
+#
+# Definitions and options specified here will be used when building local tools and
+# other code that runs on the development host, but do _NOT_ apply to flight software
+# (embedded) code or anything built for the target machine. 
+#
+# These options assume a GCC toolchain but a similar set should be applicable to clang.
+#
+add_compile_options(
+    -std=c99                # Target the C99 standard (without gcc extensions) 
+    -pedantic               # Issue all the warnings demanded by strict ISO C
+    -Wall                   # Warn about most questionable operations
+    -Wstrict-prototypes     # Warn about missing prototypes
+    -Wwrite-strings         # Warn if not treating string literals as "const"
+    -Wpointer-arith         # Warn about suspicious pointer operations
+    -Werror                 # Treat warnings as errors (code should be clean) 
+)
+
+# The _XOPEN_SOURCE directive is required for glibc to enable conformance with the
+# the X/Open standard version 6, which includes POSIX.1c as well as SUSv2/UNIX98 extensions.
+add_definitions(
+    -D_XOPEN_SOURCE=600
+)