gnu: GCC: Add cross environment variables patch to GCC 12.

* gnu/packages/patches/gcc-12-cross-environment-variables.patch : New file.
* gnu/local.mk (dist_patch_DATA): Add
gcc-12-cross-environment-variables.patch.
* gnu/packages/cross-base.scm (cross-gcc)[source](patches): Apply the patch.

Signed-off-by: Ludovic Courtès <ludo@gnu.org>

gnu/local.mk

@@ -1131,6 +1131,7 @@ dist_patch_DATA =						\
   %D%/packages/patches/gcc-9-strmov-store-file-names.patch	\
   %D%/packages/patches/gcc-12-strmov-store-file-names.patch	\
   %D%/packages/patches/gcc-10-cross-environment-variables.patch \
+  %D%/packages/patches/gcc-12-cross-environment-variables.patch \
   %D%/packages/patches/gcolor3-update-libportal-usage.patch	\
   %D%/packages/patches/gd-fix-tests-on-i686.patch		\
   %D%/packages/patches/gd-brect-bounds.patch			\

gnu/packages/cross-base.scm

@@ -242,6 +242,9 @@ (define* (cross-gcc target
         (append
          (origin-patches (package-source xgcc))
          (append (cond
+                  ((version>=? (package-version xgcc) "12.0")
+                   (search-patches "gcc-12-cross-environment-variables.patch"
+                                   "gcc-cross-gxx-include-dir.patch"))
                   ((version>=? (package-version xgcc) "10.0")
                    (search-patches "gcc-10-cross-environment-variables.patch"
                                    "gcc-cross-gxx-include-dir.patch"))

gnu/packages/patches/gcc-12-cross-environment-variables.patch

@@ -0,0 +1,54 @@
+Search path environment variables for cross-compilers.  See the discussion
+at <http://gcc.gnu.org/ml/gcc/2013-02/msg00124.html>.
+
+Note: Touch 'C_INCLUDE_PATH' et al. rather than 'CPATH', as discussed
+at <http://bugs.gnu.org/22186>.
+
+diff --git a/gcc/gcc.cc b/gcc/gcc.cc
+--- a/gcc/gcc.cc
++++ b/gcc/gcc.cc
+@@ -4832,7 +4832,7 @@ process_command (unsigned int decoded_options_count,
+     }
+ 
+   temp = env.get (LIBRARY_PATH_ENV);
+-  if (temp && *cross_compile == '0')
++  if (temp)
+     {
+       const char *startp, *endp;
+       char *nstore = (char *) alloca (strlen (temp) + 3);
+diff --git a/gcc/incpath.cc b/gcc/incpath.cc
+--- a/gcc/incpath.cc
++++ b/gcc/incpath.cc
+@@ -480,8 +480,8 @@ register_include_chains (cpp_reader *pfile, const char *sysroot,
+ 			 int stdinc, int cxx_stdinc, int verbose)
+ {
+   static const char *const lang_env_vars[] =
+-    { "C_INCLUDE_PATH", "CPLUS_INCLUDE_PATH",
+-      "OBJC_INCLUDE_PATH", "OBJCPLUS_INCLUDE_PATH" };
++    { "CROSS_C_INCLUDE_PATH", "CROSS_CPLUS_INCLUDE_PATH",
++      "CROSS_OBJC_INCLUDE_PATH", "CROSS_OBJCPLUS_INCLUDE_PATH" };
+   cpp_options *cpp_opts = cpp_get_options (pfile);
+   size_t idx = (cpp_opts->objc ? 2: 0);
+ 
+@@ -492,7 +492,7 @@ register_include_chains (cpp_reader *pfile, const char *sysroot,
+ 
+   /* CPATH and language-dependent environment variables may add to the
+      include chain.  */
+-  add_env_var_paths ("CPATH", INC_BRACKET);
++  add_env_var_paths ("CROSS_CPATH", INC_BRACKET);
+   add_env_var_paths (lang_env_vars[idx], INC_SYSTEM);
+ 
+   target_c_incpath.extra_pre_includes (sysroot, iprefix, stdinc);
+diff --git a/gcc/system.h b/gcc/system.h
+--- a/gcc/system.h
++++ b/gcc/system.h
+@@ -1317,4 +1317,6 @@ endswith (const char *str, const char *suffix)
+   return memcmp (str + str_len - suffix_len, suffix, suffix_len) == 0;
+ }
+ 
++#define LIBRARY_PATH_ENV "CROSS_LIBRARY_PATH"
++
+ #endif /* ! GCC_SYSTEM_H */
+-- 
+2.36.1
+