move `CMAKE_POSITION_INDEPENDENT_CODE` to Makefile

This is where I originally meant the directive to go, but it didn't seem to work
the first time I tried it, hence the added lines in wasi-sdk.cmake and
wasi-sdk-pthread.cmake.  However, it seems to work fine now, so I'm switching it
back to be consistent with other similar CMake flags.

Signed-off-by: Joel Dice <joel.dice@fermyon.com>

Makefile

@@ -163,6 +163,7 @@ LIBCXX_CMAKE_FLAGS = \
     -DCMAKE_MODULE_PATH=$(ROOT_DIR)/cmake \
     -DCMAKE_TOOLCHAIN_FILE=$(ROOT_DIR)/wasi-sdk.cmake \
     -DCMAKE_STAGING_PREFIX=$(PREFIX)/share/wasi-sysroot \
+    -DCMAKE_POSITION_INDEPENDENT_CODE=$(2) \
     -DLLVM_CONFIG_PATH=$(ROOT_DIR)/build/llvm/bin/llvm-config \
     -DCMAKE_VERBOSE_MAKEFILE:BOOL=ON \
     -DCXX_SUPPORTS_CXX11=ON \

wasi-sdk-pthread.cmake

@@ -41,5 +41,3 @@ set(CMAKE_FIND_ROOT_PATH_MODE_PROGRAM NEVER)
 set(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY)
 set(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)
 set(CMAKE_FIND_ROOT_PATH_MODE_PACKAGE ONLY)
-
-set(CMAKE_POSITION_INDEPENDENT_CODE On)

wasi-sdk.cmake

@@ -38,5 +38,3 @@ set(CMAKE_FIND_ROOT_PATH_MODE_PROGRAM NEVER)
 set(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY)
 set(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)
 set(CMAKE_FIND_ROOT_PATH_MODE_PACKAGE ONLY)
-
-set(CMAKE_POSITION_INDEPENDENT_CODE On)