build/cmake/stdlib: guard include/cxx by LIBMINIABI, fix div_t conflict

include/cxx contains NuttX's mini C++ ABI shims and must only be added
to the include path when CONFIG_LIBMINIABI is selected.  tools/Config.mk
was adding it unconditionally for every non-LIBCXX/non-UCLIBCXX build,
and the platform.cmake files for arm, arm64, risc-v, x86_64 and tricore
were adding it inside the CONFIG_LIBCXXTOOLCHAIN block.

With an unpatched downloaded ARM GNU Toolchain, <cstdlib> uses
newlib's stdlib.h, defining div_t as an anonymous struct.  A later
inclusion of NuttX's stdlib.h via <cstdio>->stdio.h->kmalloc.h then
redefines div_t with struct tag div_s, causing a conflicting declaration
error.

Guard the div_t/ldiv_t/lldiv_t definitions in stdlib.h with
redefinitions when a toolchain stdlib.h was already processed.

Also fix lldiv_s members typed as long instead of long long.

Signed-off-by: trns1997 <trns1997@gmail.com>

arch/arm/src/cmake/platform.cmake

@@ -87,6 +87,9 @@ endif()
 
 if(CONFIG_LIBCXXTOOLCHAIN)
   nuttx_find_toolchain_lib(libstdc++.a)
+endif()
+
+if(CONFIG_LIBMINIABI)
   list(APPEND CMAKE_CXX_STANDARD_INCLUDE_DIRECTORIES ${NUTTX_DIR}/include/cxx)
 endif()
 

arch/arm64/src/cmake/platform.cmake

@@ -47,6 +47,9 @@ endif()
 
 if(CONFIG_LIBCXXTOOLCHAIN)
   nuttx_find_toolchain_lib(libstdc++.a)
+endif()
+
+if(CONFIG_LIBMINIABI)
   list(APPEND CMAKE_CXX_STANDARD_INCLUDE_DIRECTORIES ${NUTTX_DIR}/include/cxx)
 endif()
 

arch/risc-v/src/cmake/platform.cmake

@@ -49,6 +49,9 @@ endif()
 
 if(CONFIG_LIBCXXTOOLCHAIN)
   nuttx_find_toolchain_lib(libstdc++.a)
+endif()
+
+if(CONFIG_LIBMINIABI)
   list(APPEND CMAKE_CXX_STANDARD_INCLUDE_DIRECTORIES ${NUTTX_DIR}/include/cxx)
 endif()
 

arch/tricore/src/cmake/platform.cmake

@@ -49,6 +49,8 @@ if(CONFIG_TRICORE_TOOLCHAIN_GNU)
   endif()
   if(CONFIG_LIBCXXTOOLCHAIN)
     nuttx_find_toolchain_lib(libstdc++.a)
+  endif()
+  if(CONFIG_LIBMINIABI)
     list(APPEND CMAKE_CXX_STANDARD_INCLUDE_DIRECTORIES ${NUTTX_DIR}/include/cxx)
   endif()
   if(CONFIG_COVERAGE_TOOLCHAIN)

arch/x86_64/src/cmake/platform.cmake

@@ -49,6 +49,9 @@ endif()
 
 if(CONFIG_LIBCXXTOOLCHAIN)
   nuttx_find_toolchain_lib(libstdc++.a)
+endif()
+
+if(CONFIG_LIBMINIABI)
   list(APPEND CMAKE_CXX_STANDARD_INCLUDE_DIRECTORIES ${NUTTX_DIR}/include/cxx)
 endif()
 

include/stdlib.h

@@ -87,8 +87,23 @@
  * Public Type Definitions
  ****************************************************************************/
 
-/* Structure type returned by the div() function. */
+/* Structure type returned by the div() function.
+ *
+ * When CONFIG_LIBCXXTOOLCHAIN is active the toolchain's <cstdlib> uses
+ * #include_next <stdlib.h> which bypasses this file and lands on the
+ * toolchain's own stdlib.h (e.g. newlib's _STDLIB_H_ guard).  That file
+ * defines div_t/ldiv_t/lldiv_t with an anonymous struct that GCC internally
+ * names struct div_t.  A subsequent inclusion of this file (through the
+ * cstdio -> stdio.h -> kmalloc.h chain) would then attempt to redefine the
+ * same typedef with a different struct tag, causing a "conflicting
+ * declaration" error.  Guard against that by skipping our own struct/typedef
+ * definitions when a toolchain stdlib.h has already been included.
+ *
+ * _STDLIB_H_  - newlib (ARM GNU Toolchain, picolibc, avr-libc, ...)
+ * _STDLIB_H   - glibc / musl (native host toolchains)
+ */
 
+#if !defined(_STDLIB_H_) && !defined(_STDLIB_H)
 struct div_s
 {
   int quot;     /* Quotient */
@@ -111,11 +126,12 @@ typedef struct ldiv_s ldiv_t;
 
 struct lldiv_s
 {
-  long quot;    /* Quotient */
-  long rem;     /* Remainder */
+  long long quot;    /* Quotient */
+  long long rem;     /* Remainder */
 };
 
 typedef struct lldiv_s lldiv_t;
+#endif /* !defined(_STDLIB_H_) && !defined(_STDLIB_H) */
 
 /****************************************************************************
  * Public Function Prototypes

tools/Config.mk

@@ -746,7 +746,9 @@ ifeq ($(CONFIG_LIBCXX),y)
   ARCHXXINCLUDES += ${INCSYSDIR_PREFIX}$(TOPDIR)$(DELIM)include$(DELIM)libcxx
 else ifeq ($(CONFIG_UCLIBCXX),y)
   ARCHXXINCLUDES += ${INCSYSDIR_PREFIX}$(TOPDIR)$(DELIM)include$(DELIM)uClibc++
-else
+endif
+
+ifeq ($(CONFIG_LIBMINIABI),y)
   ARCHXXINCLUDES += ${INCSYSDIR_PREFIX}$(TOPDIR)$(DELIM)include$(DELIM)cxx
   ifeq ($(CONFIG_ETL),y)
     ARCHXXINCLUDES += ${INCSYSDIR_PREFIX}$(TOPDIR)$(DELIM)include$(DELIM)etl