Improve handling of platform-specific build options (#2162)

* Opt into POSIX functions with `_POSIX_C_SOURCE` before any system
  headers are `#include`d
* Allow user to override `make develop`'s `WARNFLAGS` and `CXXFLAGS`
* Use `make develop` on 32-bit Cygwin with sanitizers disabled
* Do not unnecessarily redefine `fseek` and `ftell`
* Disable a false-positive `-Wno-null-dereference` on 32-bit Cygwin

Co-authored-by: ISSOtm <[email protected]>

src/link/assign.cpp

@@ -1,5 +1,7 @@
 // SPDX-License-Identifier: MIT
 
+#include "platform.hpp"
+
 #include "link/assign.hpp"
 
 #include <algorithm>
@@ -16,7 +18,6 @@
 #include "helpers.hpp"
 #include "itertools.hpp"
 #include "linkdefs.hpp"
-#include "platform.hpp"
 #include "verbosity.hpp"
 
 #include "link/main.hpp"

src/link/object.cpp

@@ -1,5 +1,7 @@
 // SPDX-License-Identifier: MIT
 
+#include "platform.hpp"
+
 #include "link/object.hpp"
 
 #include <deque>
@@ -18,7 +20,6 @@
 
 #include "helpers.hpp"
 #include "linkdefs.hpp"
-#include "platform.hpp"
 #include "util.hpp" // xfclose
 #include "verbosity.hpp"
 #include "version.hpp"

src/link/output.cpp

@@ -1,5 +1,7 @@
 // SPDX-License-Identifier: MIT
 
+#include "platform.hpp"
+
 #include "link/output.hpp"
 
 #include <algorithm>
@@ -19,7 +21,6 @@
 #include "extern/utf8decoder.hpp"
 #include "helpers.hpp"
 #include "linkdefs.hpp"
-#include "platform.hpp"
 #include "util.hpp"
 
 #include "link/main.hpp"

src/link/sdas_obj.cpp

@@ -1,5 +1,7 @@
 // SPDX-License-Identifier: MIT
 
+#include "platform.hpp"
+
 #include "link/sdas_obj.hpp"
 
 #include <inttypes.h>
@@ -14,7 +16,6 @@
 
 #include "helpers.hpp" // assume, literal_strlen
 #include "linkdefs.hpp"
-#include "platform.hpp"
 #include "util.hpp" // parseWholeNumber
 
 #include "link/fstack.hpp"