cgo: support builtin #include headers

Add support for header files bundled with the compiler by copying them
into the release tarball.

testdata/cgo/main.c

@@ -1,8 +1,8 @@
 #include "main.h"
 
 int global = 3;
-_Bool globalBool = 1;
-_Bool globalBool2 = 10; // test narrowing
+bool globalBool = 1;
+bool globalBool2 = 10; // test narrowing
 float globalFloat = 3.1;
 double globalDouble = 3.2;
 _Complex float globalComplexFloat = 4.1+3.3i;
@@ -11,6 +11,7 @@ _Complex double globalComplexLongDouble = 4.3+3.5i;
 char globalChar = 100;
 void *globalVoidPtrSet = &global;
 void *globalVoidPtrNull;
+int64_t globalInt64 = -(2LL << 40);
 collection_t globalStruct = {256, -123456, 3.14, 88};
 int globalStructSize = sizeof(globalStruct);
 short globalArray[3] = {5, 6, 7};

testdata/cgo/main.go

@@ -43,6 +43,7 @@ func main() {
 	println("char match:", C.globalChar == 100)
 	var voidPtr unsafe.Pointer = C.globalVoidPtrNull
 	println("void* match:", voidPtr == nil, C.globalVoidPtrNull == nil, (*C.int)(C.globalVoidPtrSet) == &C.global)
+	println("int64_t match:", C.globalInt64 == C.int64_t(-(2<<40)))
 
 	// complex types
 	println("struct:", C.int(unsafe.Sizeof(C.globalStruct)) == C.globalStructSize, C.globalStruct.s, C.globalStruct.l, C.globalStruct.f)

testdata/cgo/main.h

@@ -1,3 +1,6 @@
+#include <stdbool.h>
+#include <stdint.h>
+
 typedef short myint;
 int add(int a, int b);
 typedef int (*binop_t) (int, int);
@@ -27,10 +30,10 @@ void unionSetShort(short s);
 void unionSetFloat(float f);
 void unionSetData(short f0, short f1, short f2);
 
-// test globals
+// test globals and datatypes
 extern int global;
-extern _Bool globalBool;
-extern _Bool globalBool2;
+extern bool globalBool;
+extern bool globalBool2;
 extern float globalFloat;
 extern double globalDouble;
 extern _Complex float globalComplexFloat;
@@ -39,6 +42,7 @@ extern _Complex double globalComplexLongDouble;
 extern char globalChar;
 extern void *globalVoidPtrSet;
 extern void *globalVoidPtrNull;
+extern int64_t globalInt64;
 extern collection_t globalStruct;
 extern int globalStructSize;
 extern short globalArray[3];

testdata/cgo/out.txt

@@ -16,6 +16,7 @@ complex double: (+4.200000e+000+3.400000e+000i)
 complex long double: (+4.300000e+000+3.500000e+000i)
 char match: true
 void* match: true true true
+int64_t match: true
 struct: true 256 -123456 +3.140000e+000
 array: 5 6 7
 union: true