Add flag to rgbasm to disable LD->LDH optimization

rgbasm tries to optimize any loads from/to $FF00-$FFFF and generate
LDH 2-byte opcodes instead of regular LD 3-byte opcodes. This is a bit
inconsistent as it only works for constant values. If a load is trying
to access a label in a HRAM floating section, or a section found in a
different object file, this optimization doesn't work.

This means that a simple refactor or code could allow rgbasm to perform
the optimzation or prevent it from doing so. For certain projects, like
disassemblies, this is a problem.

This patch adds flag -L to rgbasm to disable the optimization, and
doesn't change the behaviour of any other existing code.

Signed-off-by: Antonio Niño Díaz <antonio_nd@outlook.com>

docs/rgbasm.1.html

@@ -27,7 +27,7 @@
 <table class="Nm">
   <tr>
     <td><b class="Nm" title="Nm">rgbasm</b></td>
-    <td>[<span class="Op"><b class="Fl" title="Fl">-EhVvw</b></span>]
+    <td>[<span class="Op"><b class="Fl" title="Fl">-EhLVvw</b></span>]
       [<span class="Op"><b class="Fl" title="Fl">-b</b>
       <var class="Ar" title="Ar">chars</var></span>]
       [<span class="Op"><b class="Fl" title="Fl">-D</b>
@@ -89,6 +89,13 @@ The <b class="Nm" title="Nm">rgbasm</b> program creates an object file from an
   <dd class="It-tag">Add an include path.</dd>
   <dt class="It-tag">&#x00A0;</dt>
   <dd class="It-tag">&#x00A0;</dd>
+  <dt class="It-tag"><a class="selflink" href="#L"><b class="Fl" title="Fl" id="L">-L</b></a></dt>
+  <dd class="It-tag">Disable the optimization that turns loads of the form
+      <b class="Sy" title="Sy">LD [$FF00+n8],A</b> into the opcode
+      <b class="Sy" title="Sy">LDH [$FF00+n8],A</b> in order to have full
+      control of the result in the final ROM.</dd>
+  <dt class="It-tag">&#x00A0;</dt>
+  <dd class="It-tag">&#x00A0;</dd>
   <dt class="It-tag"><a class="selflink" href="#M"><b class="Fl" title="Fl" id="M">-M</b></a>
     <var class="Ar" title="Ar">dependfile</var></dt>
   <dd class="It-tag">Print <a class="Xr" title="Xr">make(1)</a> dependencies to
@@ -120,7 +127,11 @@ The <b class="Nm" title="Nm">rgbasm</b> program creates an object file from an
 <h1 class="Sh" title="Sh" id="EXAMPLES"><a class="selflink" href="#EXAMPLES">EXAMPLES</a></h1>
 Assembling a basic source file is simple:
 <div class="Pp"></div>
-<div class="D1">$ rgbasm -o bar.o foo.asm</div>
+<div class="Bd" style="margin-left: 5.00ex;">
+<pre class="Li">
+$ rgbasm -o bar.o foo.asm
+</pre>
+</div>
 <div class="Pp"></div>
 The resulting object file is not yet a usable ROM image &#x2014; it must first
   be run through <a class="Xr" title="Xr">rgblink(1)</a> and
@@ -138,7 +149,7 @@ The resulting object file is not yet a usable ROM image &#x2014; it must first
   <a class="Lk" title="Lk" href="https://github.com/rednex/rgbds">https://github.com/rednex/rgbds</a>.</div>
 <table class="foot">
   <tr>
-    <td class="foot-date">January 26, 2018</td>
+    <td class="foot-date">February 24, 2018</td>
     <td class="foot-os">RGBDS Manual</td>
   </tr>
 </table>

docs/rgbasm.5.html

@@ -125,7 +125,10 @@ Possible section types are as follows:
       <b class="Sy" title="Sy">LDH [$FF00+n8],A</b> and
       <b class="Sy" title="Sy">LDH A,[$FF00+n8]</b> syntax instead. This forces
       the assembler to emit the correct instruction and the linker to check if
-      the value is in the correct range.</dd>
+      the value is in the correct range. This optimization can be disabled by
+      passing the <b class="Fl" title="Fl">-L</b> flag to
+      <b class="Sy" title="Sy">rgbasm</b> as explained in
+      <a class="Xr" title="Xr">rgbasm(1)</a>.</dd>
 </dl>
 <div class="Pp"></div>
 A section is usually defined as a floating one, but the code can restrict where
@@ -1462,7 +1465,7 @@ The options that OPT can modify are currently: <b class="Sy" title="Sy">b</b>,
   <a class="Lk" title="Lk" href="https://github.com/rednex/rgbds">https://github.com/rednex/rgbds</a>.</div>
 <table class="foot">
   <tr>
-    <td class="foot-date">January 27, 2018</td>
+    <td class="foot-date">February 24, 2018</td>
     <td class="foot-os">RGBDS Manual</td>
   </tr>
 </table>

docs/rgbds.7.html

@@ -26,9 +26,13 @@
 <h1 class="Sh" title="Sh" id="EXAMPLES"><a class="selflink" href="#EXAMPLES">EXAMPLES</a></h1>
 To get a working ROM image from a single assembly source file:
 <div class="Pp"></div>
-<div class="D1">$ rgbasm -o bar.o foo.asm</div>
-<div class="D1">$ rgblink -o baz.gb bar.o</div>
-<div class="D1">$ rgbfix -v -p 0 baz.gb</div>
+<div class="Bd" style="margin-left: 5.00ex;">
+<pre class="Li">
+$ rgbasm -o bar.o foo.asm 
+$ rgblink -o baz.gb bar.o 
+$ rgbfix -v -p 0 baz.gb
+</pre>
+</div>
 <h1 class="Sh" title="Sh" id="SEE_ALSO"><a class="selflink" href="#SEE_ALSO">SEE
   ALSO</a></h1>
 <a class="Xr" title="Xr">rgbasm(1)</a>, <a class="Xr" title="Xr">rgbfix(1)</a>,
@@ -58,7 +62,7 @@ To get a working ROM image from a single assembly source file:
 </div>
 <table class="foot">
   <tr>
-    <td class="foot-date">January 26, 2018</td>
+    <td class="foot-date">February 24, 2018</td>
     <td class="foot-os">RGBDS Manual</td>
   </tr>
 </table>