[SCons] Change icc compilation options

* -vec-report0 is deprecated
* -diag-disable 1478 is not needed (has no effect)
* `Wcheck` (perform compile-time code checking for certain code) is
  changed to to `Wall` (enable warning and error diagnostics) as most
  warnings are due to upstream issues in fmtlib
* disable fast math optimization

Beyond, fix CYTHON_FALLTHROUGH for icc

SConstruct

@@ -212,7 +212,6 @@ config_options = [
            optimization level.""",
         {
             "cl": "/MD /nologo /D_SCL_SECURE_NO_WARNINGS /D_CRT_SECURE_NO_WARNINGS",
-            "icc": "-vec-report0 -diag-disable 1478",
             "clang": "-fcolor-diagnostics",
             "default": "",
         }),
@@ -443,6 +442,7 @@ config_options = [
         "Additional compiler flags passed to the C/C++ compiler when 'optimize=yes'.",
         {
             "cl": "/O2",
+            "icc": "-O3 -fp-model precise",
             "icx": "-O3 -fp-model precise", # cannot assume finite math
             "gcc": "-O3 -Wno-inline",
             "default": "-O3",

interfaces/cython/SConscript

@@ -70,6 +70,9 @@ if (
 if localenv["HAS_CLANG"] and py_version_short == parse_version("3.8"):
     localenv.Append(CXXFLAGS='-Wno-deprecated-declarations')
 
+if "icc" in localenv["CC"]:
+    localenv.Append(CPPDEFINES={"CYTHON_FALLTHROUGH":" __attribute__((fallthrough))"})
+
 if localenv['OS'] == 'Darwin':
     localenv.Append(LINKFLAGS='-undefined dynamic_lookup')
 elif localenv['OS'] == 'Windows':