patch 8.2.1648: Amiga: no common build file for Amiga (-like) systems

Problem:    Amiga: no common build file for Amiga (-like) systems.
Solution:   Turn Make_morph.mak into Make_ami.mak. (Ola Söder, closes #6805)
diff --git a/src/INSTALLami.txt b/src/INSTALLami.txt
index 0acd6fd..a2c9faf 100644
--- a/src/INSTALLami.txt
+++ b/src/INSTALLami.txt
@@ -1,4 +1,4 @@
-INSTALLami.txt - Installation of Vim from source on Amiga
+INSTALLami.txt - Installation of Vim from source on Amiga and MorphOS
 
 This file contains instructions for compiling Vim. If you already have an
 executable version of Vim, you don't need this.
@@ -7,28 +7,13 @@
 this, then you will get the default behavior as is documented, which should
 be fine for most people.
 
-
 Summary:
-make -f Make_manx.mak		Manx C
-make -f Make_sas.mak		Lattice/SAS C
-make -f Make_dice.mak		DICE
+make -f Make_ami.mak        gcc
+make -f Make_ami.mak CC=vc  vbcc
 
-The Manx compiler is preferred, it was used to produce the Amiga executable
-and has been tested most. You should not get any errors or warnings.
+Please note that currently only gcc has been tested. VBCC would need its own
+CFLAGS, but should otherwise work out of the box. For cross-compiling, UNM
+can be used to override uname and thereby set the target. An example is shown
+below:
 
-The SAS compiler can be used. Older versions (6.0 to 6.3) don't work with the
-optimizer switched on. This seems to be fixed with 6.5 or 6.56, but this has
-not been tested much.  Also disable optimizing when the compiler runs out of
-memory or crashes the system (yes, that happens; did I say the Manx compiler
-is preferred?).
-
-The DICE makefile has been reported to work by one person only.
-
-You will have to set the "VIM" environment variable to the location of the
-documentation files.
-
-
-MorphOS
-
-Use the Make_morph.mak Makefile:
-	make -f Make_morph.mak
+make -f Make_ami.mak CC=ppc-morphos-gcc UNM=MorphOS