Fix endianness issue in dtoa.cpp

[jamesjer]

Define IEEE_MC68k instead of IEEE_8087 on big endian architectures.

Fixes #183. All tests pass on s390x with this patch. The unconditional #define IEEE_8087 does not seem to be present in the AMPL ASL git repository, so it appears to be a SCIP addition. You might prefer to remove that addition, and instead use cmake to add either -DIEEE_8087 or -DIEEE_MC68k to the build flags.

[jamesjer]

The other approach I mentioned would look like this. Let me know if you prefer that approach and I will update this PR.

diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index c6ce72830c..9892c9776c 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -12,6 +12,12 @@ set(CMAKE_C_STANDARD 99)
 set(CMAKE_C_STANDARD_REQUIRED on)
 set(CMAKE_C_EXTENSIONS OFF)
 
+if(CMAKE_CXX_BYTE_ORDER STREQUAL "BIG_ENDIAN")
+    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -DIEEE_MC68k")
+else()
+    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -DIEEE_8087")
+endif()
+
 if(NOT WIN32)
     set(SCIP_COMP_OPTIONS ${SCIP_COMP_OPTIONS} "$<$<COMPILE_LANGUAGE:C>:-D_XOPEN_SOURCE=600>")
 endif()
diff --git a/src/amplmp/src/dtoa.cpp b/src/amplmp/src/dtoa.cpp
index 3386cea500..9c064d308a 100644
--- a/src/amplmp/src/dtoa.cpp
+++ b/src/amplmp/src/dtoa.cpp
@@ -349,8 +349,6 @@ static double private_mem[PRIVATE_mem], *pmem_next = private_mem;
 extern "C" {
 #endif
 
-#define IEEE_8087
-#define IEEE_Arith
 #if defined(IEEE_8087) + defined(IEEE_MC68k) + defined(VAX) + defined(IBM) != 1
 Exactly one of IEEE_8087, IEEE_MC68k, VAX, or IBM should be defined.
 #endif