cmake: For gcc8 use linker to find paths to libc, libm, libstdc++, etc

Removes the need to know/guess the paths to these libraries. Once we are gcc 8 only, we
can remove -nostdlib and no additional arguments are needed for system libraries.

The catch is: any time IDF overrides a symbol in the toolchain sysroot, we need
an undefined linker marker to make sure this symbol is seen by linker.

components/esp32/CMakeLists.txt

@@ -88,4 +88,13 @@ else()
         cpu_start.c
         PROPERTIES COMPILE_FLAGS
         -fno-stack-protector)
+
+    if(CONFIG_SPIRAM_CACHE_WORKAROUND)
+        # Note: Adding as a PUBLIC compile option here causes this option to propagate to all components that depend on esp32.
+        #
+        # To handle some corner cases, the same flag is set in project_include.cmake
+        target_compile_options(${COMPONENT_LIB} PUBLIC -mfix-esp32-psram-cache-issue)
+        # also, make sure we link with this option so correct toolchain libs are pulled in
+        target_link_libraries(${COMPONENT_LIB} -mfix-esp32-psram-cache-issue)
+    endif()
 endif()

components/esp32/ld/esp32.project.ld.in

@@ -267,12 +267,12 @@ SECTIONS
     __eh_frame = ABSOLUTE(.);
     KEEP(*(.eh_frame))
     . = (. + 7) & ~ 3;
-    /*  C++ constructor and destructor tables, properly ordered:  */
+    /*  C++ constructor and destructor tables
+
+        Make a point of not including anything from crtbegin.o or crtend.o, as IDF doesn't use toolchain crt
+      */
     __init_array_start = ABSOLUTE(.);
-    KEEP (*crtbegin.*(.ctors))
-    KEEP (*(EXCLUDE_FILE (*crtend.*) .ctors))
-    KEEP (*(SORT(.ctors.*)))
-    KEEP (*(.ctors))
+    KEEP (*(EXCLUDE_FILE (*crtend.* *crtbegin.*) .ctors .ctors.*))
     __init_array_end = ABSOLUTE(.);
     KEEP (*crtbegin.*(.dtors))
     KEEP (*(EXCLUDE_FILE (*crtend.*) .dtors))