Minor build fixes for CMake and libssl on x86 (#2267)

### Description of changes: 
* Removes unnecessary variable evaluation in a handful of if statements
for `CMAKE_SYSTEM_PROCESSOR_LOWER`. These can result in a failure if
`CMAKE_SYSTEM_PROCESSOR_LOWER` is an empty string as the `${}` is
expanded first in the if-statement due to historical reasons.
* `libssl` can fail to compile if building on x86 since we don't pass
`-msse2` to the C++ compiler. This is due to the fact that the
`crypto/internal.h` is included by libssl and it explicitly checks for
SSE2 support. See
https://github.com/aws/aws-lc/blob/main/crypto/internal.h#L203-L214

### Testing
* Verified build with a modified `./util/32-bit-toolchain.cmake` that
only sets `-m32` (since building on an x86-64 platform).

By submitting this pull request, I confirm that my contribution is made
under the terms of the Apache 2.0 license and the ISC license.

Author: skmcgrail

CMakeLists.txt

@@ -844,11 +844,11 @@ elseif(CMAKE_SYSTEM_PROCESSOR_LOWER MATCHES "^arm*")
   set(ARCH "arm")
 elseif(CMAKE_SYSTEM_PROCESSOR_LOWER MATCHES "powerpc64le|ppc64le")
   set(ARCH "ppc64le")
-elseif (${CMAKE_SYSTEM_PROCESSOR_LOWER} STREQUAL "riscv64")
+elseif(CMAKE_SYSTEM_PROCESSOR_LOWER STREQUAL "riscv64")
   set(ARCH "riscv64")
-elseif (${CMAKE_SYSTEM_PROCESSOR_LOWER} STREQUAL "s390x")
+elseif(CMAKE_SYSTEM_PROCESSOR_LOWER STREQUAL "s390x")
   set(ARCH "s390x")
-elseif (${CMAKE_SYSTEM_PROCESSOR_LOWER} STREQUAL "loongarch64")
+elseif(CMAKE_SYSTEM_PROCESSOR_LOWER STREQUAL "loongarch64")
   set(ARCH "loongarch64")
 else()
   message(STATUS "Unknown processor found. Using generic implementations. Processor: " ${CMAKE_SYSTEM_PROCESSOR})
@@ -862,6 +862,8 @@ if(ARCH STREQUAL "x86" AND NOT OPENSSL_NO_SSE2_FOR_TESTING)
   # See: https://github.com/aws/aws-lc/commit/6fe8dcbe96e580ea85233fdb98a142e42951b70b
   if(GCC OR CLANG)
     set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -msse2")
+    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -msse2")
+    set(CMAKE_ASM_FLAGS "${CMAKE_ASM_FLAGS} -msse2")
   endif()
 endif()