[Issue 23547] New: [REG master] C header files have precedent over D modules

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=23547

          Issue ID: 23547
           Summary: [REG master] C header files have precedent over D
                    modules
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: regression
          Priority: P1
         Component: dmd
          Assignee: nobody at puremagic.com
          Reporter: ibuclaw at gdcproject.org

This test fails.

$ dmd -I=imports importd.d
importd.d(2): Error: undefined identifier `Have_Qsort_R`
importd.d(2):        while evaluating: `static assert(Have_Qsort_R)`


importd.d
```
import gcc.config;
static assert(Have_Qsort_R);
```

imports/gcc/config.d
```
module gcc.config;
enum Have_Qsort_R = true;
```

gcc/config.h
```
#ifndef GCC_CONFIG_H
#define GCC_CONFIG_H
#ifdef GENERATOR_FILE
#error config.h is for the host, not build, machine.
#endif
#ifdef IN_GCC
# include "ansidecl.h"
#endif
#endif /* GCC_CONFIG_H */
```

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