[flang][cuda][NFC] Add missing default values (#117610)

Make it homogenous with other runtime entry points.

Author: clementval

flang/include/flang/Runtime/CUDA/allocatable.h

@@ -25,14 +25,16 @@ int RTDECL(CUFAllocatableAllocate)(Descriptor &, bool hasStat = false,
 /// Perform allocation of the descriptor without synchronization. Assign data
 /// from source.
 int RTDEF(CUFAllocatableAllocateSource)(Descriptor &alloc,
-    const Descriptor &source, bool hasStat, const Descriptor *errMsg,
-    const char *sourceFile, int sourceLine);
+    const Descriptor &source, bool hasStat = false,
+    const Descriptor *errMsg = nullptr, const char *sourceFile = nullptr,
+    int sourceLine = 0);
 
 /// Perform allocation of the descriptor with synchronization of it when
 /// necessary. Assign data from source.
 int RTDEF(CUFAllocatableAllocateSourceSync)(Descriptor &alloc,
-    const Descriptor &source, bool hasStat, const Descriptor *errMsg,
-    const char *sourceFile, int sourceLine);
+    const Descriptor &source, bool hasStat = false,
+    const Descriptor *errMsg = nullptr, const char *sourceFile = nullptr,
+    int sourceLine = 0);
 
 /// Perform deallocation of the descriptor with synchronization of it when
 /// necessary.