Fix pip install static library not found errors for conda (#2683)

Under certain circumstances Py_ENABLE_SHARED would be False but the static library cannot be found. For example, if you use conda environments or if you use specific versions of MacOS #2109, #2270. pip install would fail in such a situation.

In this PR, we adjust the configurations so that the installation script would attempt to use shared library instead of the static one if no static library is found. This fixes pip install for Python 3.10.15 | packaged by conda-forge. It's not clear if this would fix the MacOS problems mentioned in the above issues though, as I am unable to verify those problems.

plugins/python/uwsgiplugin.py

@@ -45,7 +45,8 @@ def get_python_version():
 if not 'UWSGI_PYTHON_NOLIB' in os.environ:
     LIBS = sysconfig.get_config_var('LIBS').split() + sysconfig.get_config_var('SYSLIBS').split()
     # check if it is a non-shared build (but please, add --enable-shared to your python's ./configure script)
-    if not sysconfig.get_config_var('Py_ENABLE_SHARED'):
+    use_static_lib = not sysconfig.get_config_var('Py_ENABLE_SHARED')
+    if use_static_lib:
         libdir = sysconfig.get_config_var('LIBPL')
         # libdir does not exists, try to get it from the venv
         version = get_python_version()
@@ -75,13 +76,17 @@ def get_python_version():
                 libpath = '%s/%s' % (libdir, sysconfig.get_config_var('LIBRARY'))
         if not os.path.exists(libpath): 
             libpath = '%s/libpython%s.a' % (libdir, version)
-        LIBS.append(libpath)
-        # hack for messy linkers/compilers
-        if '-lutil' in LIBS:
-            LIBS.append('-lutil')
-        if '-lrt' in LIBS:
-            LIBS.append('-lrt')
-    else:
+
+        if os.path.exists(libpath):
+            LIBS.append(libpath)
+            # hack for messy linkers/compilers
+            if '-lutil' in LIBS:
+                LIBS.append('-lutil')
+            if '-lrt' in LIBS:
+                LIBS.append('-lrt')
+        else:
+            use_static_lib = False
+    if not use_static_lib:
         try:
             libdir = sysconfig.get_config_var('LIBDIR')
         except: