Give up on testing guc.c's behavior for "infinity" inputs.

Further buildfarm testing shows that on the machines that are failing
ac75959cd's test case, what we're actually getting from strtod("-infinity")
is a syntax error (endptr == value) not ERANGE at all.  This test case
is not worth carrying two sets of expected output for, so just remove it,
and revert commit b212245f9's misguided attempt to work around the platform
dependency.

Discussion: https://postgr.es/m/E1h33xk-0001Og-Gs@gemulon.postgresql.org

src/backend/utils/misc/guc.c

@@ -6240,15 +6240,13 @@ parse_real(const char *value, double *result, int flags, const char **hintmsg)
 	if (hintmsg)
 		*hintmsg = NULL;
 
+	errno = 0;
 	val = strtod(value, &endptr);
-	if (endptr == value)
-		return false;			/* no HINT for syntax error */
 
-	/*
+	if (endptr == value || errno == ERANGE)
-	 * We ignore strtod's errno, so that out-of-range inputs will just result
+		return false;			/* no HINT for these cases */
-	 * in zero or infinity values.  Subsequent range checks will reject those
+
-	 * if necessary.  We do need to reject NaN explicitly, however.
+	/* reject NaN (infinities will fail range checks later) */
-	 */
 	if (isnan(val))
 		return false;			/* treat same as syntax error; no HINT */
 

src/test/regress/expected/guc.out

@@ -511,8 +511,6 @@ SET seq_page_cost TO 'NaN';
 ERROR:  invalid value for parameter "seq_page_cost": "NaN"
 SET vacuum_cost_delay TO '10s';
 ERROR:  10000 ms is outside the valid range for parameter "vacuum_cost_delay" (0 .. 100)
-SET geqo_selection_bias TO '-infinity';
-ERROR:  -Infinity is outside the valid range for parameter "geqo_selection_bias" (1.5 .. 2)
 --
 -- Test DISCARD TEMP
 --

src/test/regress/sql/guc.sql

@@ -147,7 +147,6 @@ SELECT '2006-08-13 12:34:56'::timestamptz;
 -- Test some simple error cases
 SET seq_page_cost TO 'NaN';
 SET vacuum_cost_delay TO '10s';
-SET geqo_selection_bias TO '-infinity';
 
 --
 -- Test DISCARD TEMP