Merge branch 'jc/unsetenv-returns-an-int'

The compatibility implementation for unsetenv(3) were written to
mimic ancient, non-POSIX, variant seen in an old glibc; it has been
changed to return an integer to match the more modern era.

* jc/unsetenv-returns-an-int:
  unsetenv(3) returns int, not void

compat/unsetenv.c

@@ -1,6 +1,6 @@
 #include "../git-compat-util.h"
 
-void gitunsetenv (const char *name)
+int gitunsetenv(const char *name)
 {
 #if !defined(__MINGW32__)
      extern char **environ;
@@ -24,4 +24,6 @@ void gitunsetenv (const char *name)
 	  ++dst;
      }
      environ[dst] = NULL;
+
+     return 0;
 }

git-compat-util.h

@@ -729,7 +729,7 @@ char *gitmkdtemp(char *);
 
 #ifdef NO_UNSETENV
 #define unsetenv gitunsetenv
-void gitunsetenv(const char *);
+int gitunsetenv(const char *);
 #endif
 
 #ifdef NO_STRCASESTR