[HACKERS] new gcc 7.0.1 warnings

float.c: In function ‘float4out’:

float.c:382:41: warning: ‘%.*g’ directive output may be truncated writing between 1 and 310 bytes into a region of size 65 [-Wformat-truncation=]

     snprintf(ascii, MAXFLOATWIDTH + 1, "%.*g", ndig, num);

                                         ^~~~

float.c:382:5: note: ‘snprintf’ output between 2 and 311 bytes into a destination of size 65

     snprintf(ascii, MAXFLOATWIDTH + 1, "%.*g", ndig, num);

     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

float.c: In function ‘float8out_internal’:

float.c:618:42: warning: ‘%.*g’ directive output may be truncated writing between 1 and 310 bytes into a region of size 129 [-Wformat-truncation=]

     snprintf(ascii, MAXDOUBLEWIDTH + 1, "%.*g", ndig, num);

                                          ^~~~

float.c:618:5: note: ‘snprintf’ output between 2 and 311 bytes into a destination of size 129

     snprintf(ascii, MAXDOUBLEWIDTH + 1, "%.*g", ndig, num);

     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~