testsuite: Add signal checking for signal related testcase in analyzer.

- Verifed on RISC-V and x86.

gcc/testsuite/ChangeLog:

	* gcc.dg/analyzer/signal-1.c: Add dg-require-effective-target
	signal.
	* gcc.dg/analyzer/signal-2.c: Ditto.
	* gcc.dg/analyzer/signal-3.c: Ditto.
	* gcc.dg/analyzer/signal-4a.c: Ditto.
	* gcc.dg/analyzer/signal-4b.c: Ditto.
	* gcc.dg/analyzer/signal-5.c: Ditto.
	* gcc.dg/analyzer/signal-6.c: Ditto.
	* gcc.dg/analyzer/signal-exit.c: Ditto.

gcc/testsuite/gcc.dg/analyzer/signal-1.c

@@ -1,6 +1,7 @@
 /* Example of a bad call within a signal handler.
    'handler' calls 'custom_logger' which calls 'fprintf', and 'fprintf' is
    not allowed from a signal handler.  */
+/* { dg-require-effective-target signal } */
 
 #include <stdio.h>
 #include <signal.h>

gcc/testsuite/gcc.dg/analyzer/signal-2.c

@@ -1,6 +1,7 @@
 /* Example of a bad call within a signal handler.
    'handler' calls 'custom_logger' which calls 'fprintf', and 'fprintf' is
    not allowed from a signal handler.  */
+/* { dg-require-effective-target signal } */
 
 #include <stdio.h>
 #include <signal.h>

gcc/testsuite/gcc.dg/analyzer/signal-3.c

@@ -1,3 +1,4 @@
+/* { dg-require-effective-target signal } */
 #include <stdio.h>
 #include <signal.h>
 #include <stdlib.h>

gcc/testsuite/gcc.dg/analyzer/signal-4a.c

@@ -2,6 +2,7 @@
 
 /* { dg-options "-fanalyzer -fdiagnostics-show-line-numbers -fdiagnostics-path-format=inline-events -fdiagnostics-show-caret" } */
 /* { dg-enable-nn-line-numbers "" } */
+/* { dg-require-effective-target signal } */
 
 #include <stdio.h>
 #include <signal.h>

gcc/testsuite/gcc.dg/analyzer/signal-4b.c

@@ -2,6 +2,7 @@
 
 /* { dg-options "-fanalyzer -fdiagnostics-show-line-numbers -fdiagnostics-path-format=inline-events -fdiagnostics-show-caret" } */
 /* { dg-enable-nn-line-numbers "" } */
+/* { dg-require-effective-target signal } */
 
 #include <stdio.h>
 #include <signal.h>

gcc/testsuite/gcc.dg/analyzer/signal-5.c

@@ -1,4 +1,5 @@
 /* Example of other bad calls within a signal handler.  */
+/* { dg-require-effective-target signal } */
 
 #include <stdlib.h>
 #include <signal.h>

gcc/testsuite/gcc.dg/analyzer/signal-6.c

@@ -1,3 +1,4 @@
+/* { dg-require-effective-target signal } */
 #include <stdio.h>
 #include <signal.h>
 

gcc/testsuite/gcc.dg/analyzer/signal-exit.c

@@ -1,6 +1,7 @@
 /* Example of a bad call within a signal handler with replacement
    alternative.  'handler' calls 'exit', and 'exit' is not allowed
    from a signal handler.  But '_exit' is allowed.  */
+/* { dg-require-effective-target signal } */
 
 #include <signal.h>
 #include <stdlib.h>