tools: Avoid rebuilding libc and friends every single time

We do this by preserving timestamps when copying headers so CMake doesn't think they have changed.

kernel/src/arch/x86_64/PCI.cpp

@@ -1,6 +1,7 @@
 #include "arch/PCI.h"
 #include "arch/x86_64/IO.h"
 #include <luna/Check.h>
+#include <luna/Ignore.h>
 
 #define PCI_ADDRESS_PORT 0xCF8
 #define PCI_VALUE_PORT 0xCFC
@@ -30,18 +31,21 @@ namespace PCI
         return IO::inl(PCI_VALUE_PORT);
     }
 
-    void write8(const Device::Address&, u32, u8)
+    void write8(const Device::Address& address, u32 field, u8 value)
     {
+        ignore(address, field, value);
         todo();
     }
 
-    void write16(const Device::Address&, u32, u16)
+    void write16(const Device::Address& address, u32 field, u8 value)
     {
+        ignore(address, field, value);
         todo();
     }
 
-    void write32(const Device::Address&, u32, u32)
+    void write32(const Device::Address& address, u32 field, u8 value)
     {
+        ignore(address, field, value);
         todo();
     }
 }

luna/include/luna/Ignore.h

@@ -0,0 +1,5 @@
+#pragma once
+
+template <class... Args> constexpr void ignore(Args...)
+{
+}

tools/install-headers.sh

@@ -9,5 +9,5 @@ mkdir -p $LUNA_BASE
 mkdir -p $LUNA_BASE/usr/include
 mkdir -p $LUNA_BASE/usr/include/luna
 
-cp -RT libc/include/ $LUNA_BASE/usr/include
-cp -RT luna/include/luna/ $LUNA_BASE/usr/include/luna
+cp --preserve=timestamps -RT libc/include/ $LUNA_BASE/usr/include
+cp --preserve=timestamps -RT luna/include/luna/ $LUNA_BASE/usr/include/luna