build: remove set of internal CMake variable

CMAKE_EXECUTABLE_FORMAT is set by CMake based on the target.  We were setting it
in certain cases.  Uniformly rely on CMake configuring the parameter correctly.
This should have no impact on the build.

Author: compnerd

CMakeLists.txt

@@ -639,7 +639,6 @@ endif()
 
 if("${SWIFT_HOST_VARIANT_SDK}" STREQUAL "LINUX")
 
-  set(CMAKE_EXECUTABLE_FORMAT "ELF")
   set(SWIFT_HOST_VARIANT "linux" CACHE STRING
       "Deployment OS for Swift host tools (the compiler) [linux].")
 
@@ -653,7 +652,6 @@ if("${SWIFT_HOST_VARIANT_SDK}" STREQUAL "LINUX")
 
 elseif("${SWIFT_HOST_VARIANT_SDK}" STREQUAL "FREEBSD")
 
-  set(CMAKE_EXECUTABLE_FORMAT "ELF")
   set(SWIFT_HOST_VARIANT "freebsd" CACHE STRING
       "Deployment OS for Swift host tools (the compiler) [freebsd].")
 
@@ -663,7 +661,6 @@ elseif("${SWIFT_HOST_VARIANT_SDK}" STREQUAL "FREEBSD")
 
 elseif("${SWIFT_HOST_VARIANT_SDK}" STREQUAL "CYGWIN")
 
-  # set(CMAKE_EXECUTABLE_FORMAT "ELF")
   set(SWIFT_HOST_VARIANT "cygwin" CACHE STRING
       "Deployment OS for Swift host tools (the compiler) [cygwin].")
 
@@ -682,7 +679,6 @@ elseif("${SWIFT_HOST_VARIANT_SDK}" STREQUAL "WINDOWS")
 
 elseif("${SWIFT_HOST_VARIANT_SDK}" STREQUAL "HAIKU")
 
-  set(CMAKE_EXECUTABLE_FORMAT "ELF")
   set(SWIFT_HOST_VARIANT "haiku" CACHE STRING
       "Deployment OS for Swift host tools (the compiler) [haiku].")