Fix test cases that used a non-brace-enclosed expression to initialize the first element of a union.

This is not permitted under standard C, and the previous commit caused this non-standard construct to stop working.

Tests/Conformance/C4.6.3.2.CC

@@ -60,7 +60,7 @@ main ()
    unsigned long ul1 = { 42959796 };
 
    struct S struct1 = { 3, 3.3 };
-   union  U union1  = 5;
+   union  U union1  = { 5 };
    enum   E enum1   = c;
 
    int      i2  [2] = { 160, 140 };                /* define local arrays */

Tests/Conformance/C4.6.7.1.CC

@@ -5,7 +5,7 @@ union U1 { int   i;
            float f; };
 
 union U1 u1 = { 3 };
-static union U1 u2 = 5;
+static union U1 u2 = { 5 };
 
 main ()
   {

Tests/Conformance/C9.7.0.1.CC

@@ -66,7 +66,7 @@ main ()
    unsigned long  ul1 = 0x11001100;
 
    struct S s = { 5.5, 6.6 };
-   union  U u = 4.5;
+   union  U u = { 4.5 };
 
    void (*funcPtr) (void);