posix.cfg,gnu.cfg: Add (get|set)hostname functions. (#1315)

Reference for POSIX gethostname:
http://pubs.opengroup.org/onlinepubs/9699919799/functions/gethostname.html
Reference for sethostname:
http://man7.org/linux/man-pages/man2/gethostname.2.html

cfg/gnu.cfg

@@ -705,6 +705,19 @@
       <not-uninit/>
     </arg>
   </function>
+  <!-- int sethostname(const char *name, size_t len); -->
+  <function name="sethostname">
+    <noreturn>false</noreturn>
+    <returnValue type="int"/>
+    <arg nr="1">
+      <not-null/>
+      <minsize type="argvalue" arg="2"/>
+    </arg>
+    <arg nr="2">
+      <not-uninit/>
+      <valid>0:</valid>
+    </arg>
+  </function>
   <resource>
     <dealloc>close</dealloc>
     <alloc init="true">epoll_create</alloc>

cfg/posix.cfg

@@ -3849,6 +3849,19 @@ The function 'mktemp' is considered to be dangerous due to race conditions and s
     <returnValue type="void"/>
     <noreturn>false</noreturn>
   </function>
+  <!-- int gethostname(char *name, size_t len); -->
+  <function name="gethostname">
+    <noreturn>false</noreturn>
+    <returnValue type="int"/>
+    <arg nr="1">
+      <not-null/>
+      <minsize type="argvalue" arg="2"/>
+    </arg>
+    <arg nr="2">
+      <not-uninit/>
+      <valid>1:</valid>
+    </arg>
+  </function>
   <memory>
     <alloc init="true">strdup</alloc>
     <alloc init="true">strndup</alloc>

test/cfg/gnu.c

@@ -9,6 +9,15 @@
 
 #include <string.h>
 
+void bufferAccessOutOfBounds()
+{
+    char buf[2];
+    // This is valid
+    sethostname(buf, 2);
+    // cppcheck-suppress bufferAccessOutOfBounds
+    sethostname(buf, 4);
+}
+
 void leakReturnValNotUsed()
 {
     // cppcheck-suppress unreadVariable

test/cfg/posix.c

@@ -48,6 +48,10 @@ void bufferAccessOutOfBounds(int fd)
     readlinkat(1, "path", a, 5);
     // cppcheck-suppress bufferAccessOutOfBounds
     readlinkat(1, "path", a, 6);
+    // This is valid
+    gethostname(a, 5);
+    // cppcheck-suppress bufferAccessOutOfBounds
+    gethostname(a, 6);
 }
 
 void nullPointer(char *p, int fd)