[BUG] stdlib.h: system prototype

[tmedicci]

Description / Steps to reproduce the issue

The Error

While trying to build Python with system function during the pass2dep phase, it triggers the following warning (that may be treated as an error):

/home/tiago/Documents/work/espressif/projects/nuttx/nuttxspace_alfa/apps/interpreters/python/Python/Modules/posixmodule.c:6026:14: warning: implicit declaration of function 'system' [-Wimplicit-function-declaration]
 6026 |     result = system(bytes);

Although the source includes stdlib.h, it fails because __KERNEL__ is defined and, thus, the system prototype is not defined.

Why?

There is a "trap" here:
__KERNEL__ (with $(KDEFINE)) is defined in the following snippet:

pass2dep: context tools/mkdeps$(HOSTEXEEXT) tools/cnvwindeps$(HOSTEXEEXT)
	$(Q) for dir in $(KERNDEPDIRS) ; do \
		$(MAKE) -C $$dir EXTRAFLAGS="$(KDEFINE) $(EXTRAFLAGS)" depend || exit; \
	done

$(KERNDEPDIRS) includes the $(APPDIR) folder here for flat build:

ifeq ($(CONFIG_BUILD_PROTECTED),y)
USERDEPDIRS += $(APPDIR)
else ifneq ($(CONFIG_BUILD_KERNEL),y)
KERNDEPDIRS += $(APPDIR)
else
CLEANDIRS += $(APPDIR)
endif

Proposed Fixes

We should either 1) remove $(APPDIR) from $(KERNDEPDIRS) (adding it to $(USERDEPDIRS) for both PROTECTED and FLAT BUILD or 2) define the prototype at nuttx/include/stdlib.h with the following if clause (which particularly I prefer):

#if !defined(__KERNEL__) || defined(CONFIG_BUILD_FLAT)
int       system(FAR const char *cmd);
#endif

Any thoughts about it?

On which OS does this issue occur?

[OS: Linux]

What is the version of your OS?

Manjaro

NuttX Version

master

Issue Architecture

[Arch: all]

Issue Area

[Area: Kernel]

Host information

No response

Verification

• I have verified before submitting the report.