runtime: arm actually has 8-byte alignment

Specification:
https://developer.arm.com/documentation/dui0472/k/C-and-C---Implementation-Details/Basic-data-types-in-ARM-C-and-C--
There are multiple types that have an 8-byte alignment (long long,
double) so we need to use the same maximum alignment in TinyGo.

Fixing this is necessary for the precise GC.

src/runtime/arch_arm.go

@@ -9,9 +9,9 @@ const TargetBits = 32
 
 const deferExtraRegs = 0
 
-// Align on word boundary.
+// Align on the maximum alignment for this platform (double).
 func align(ptr uintptr) uintptr {
-	return (ptr + 3) &^ 3
+	return (ptr + 7) &^ 7
 }
 
 func getCurrentStackPointer() uintptr {

src/runtime/arch_cortexm.go

@@ -15,7 +15,7 @@ const deferExtraRegs = 0
 
 // Align on word boundary.
 func align(ptr uintptr) uintptr {
-	return (ptr + 3) &^ 3
+	return (ptr + 7) &^ 7
 }
 
 func getCurrentStackPointer() uintptr {