[gcc r17-2603] cobol: Enable Bison parser stack growth.

https://gcc.gnu.org/g:172f855520d9468ef7e0e8b39ba7409d68e7acc8

commit r17-2603-g172f855520d9468ef7e0e8b39ba7409d68e7acc8
Author: James K. Lowden <[email protected]>
Date:   Tue Jul 21 15:41:21 2026 -0400

    cobol: Enable Bison parser stack growth.
    
    Work around a Bison error when compiling C output with a C++ compiler.
    Although the Bison manual states that a user-defined location type
    must be trivially copyable, it nevertheless normally does not emit
    stack-growth logic if __cplusplus is defined to the preprocessor.
    Consequently a large program that drives the stack above 200 elements
    aborts with a "memory exhausted" error.
    
    To enable stack growth, define the undocumented YYLTYPE_IS_TRIVIAL
    variable.  Use a static assert to ensure the type meets the
    requirement.
    
    A patch was submitted to the Bison project that hopefully will make
    this workaround unnecessary sometime mid-century.
    
    gcc/cobol/ChangeLog:
    
            * cbldiag.h (struct cbl_loc_t): Assert is_trivially_copyable.
            * parse.y: Define YYLTYPE_IS_TRIVIAL.

Diff:
---
 gcc/cobol/cbldiag.h | 9 +++++++--
 gcc/cobol/parse.y   | 2 ++
 2 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/gcc/cobol/cbldiag.h b/gcc/cobol/cbldiag.h
index 8916a191200b..3185002b7e8d 100644
--- a/gcc/cobol/cbldiag.h
+++ b/gcc/cobol/cbldiag.h
@@ -107,8 +107,8 @@ struct cbl_loc_base_t {
 };
 struct cbl_loc_t : public cbl_loc_base_t {
 
-  cbl_loc_t() : cbl_loc_base_t{}
-  {}
+  cbl_loc_t() = default; 
+
   cbl_loc_t(   int first_line, int first_column,
                int last_line,  int last_column ) 
     : cbl_loc_base_t {
@@ -143,6 +143,11 @@ struct cbl_loc_t : public cbl_loc_base_t {
   }
 };
 
+#include <type_traits>
+/* allow relocate stack */
+static_assert(std::is_trivially_copyable<cbl_loc_t>::value,
+             "cbl_loc_t must be trivially copyable for parser stack growth");
+
 const cbl_loc_t& cobol_location();
 
 /*
diff --git a/gcc/cobol/parse.y b/gcc/cobol/parse.y
index 05ce448f7036..5739ff14e65a 100644
--- a/gcc/cobol/parse.y
+++ b/gcc/cobol/parse.y
@@ -355,6 +355,8 @@ class locale_tgt_t {
 #include "../../libgcobol/common-defs.h"
 #include "util.h"
 #include "cbldiag.h"
+/* allow relocate stack - verifying assert in cbldiag.h */
+#define YYLTYPE_IS_TRIVIAL 1
 #include "symbols.h"
 #include "inspect.h"
 #include "../../libgcobol/io.h"